Copy on Write Snapshot

MK-95RD277-03

Hitachi TagmaStore®

Universal Storage Platform and Network Storage Controller Copy-on-Write Snapshot User's Guide

Hitachi TagmaStore® USP and NSC Copy-on-Write Snapshot User’s Guide iii

Copyright© 2006 Hitachi Data Systems Corporation, ALL RIGHTS RESERVED

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This document contains the most current information available at the time of publication. When new and/or revised information becomes available, this entire document will be updated and distributed to all registered users.

Trademarks

Hitachi Data Systems is a registered trademark and service mark of Hitachi, Ltd., and the Hitachi Data Systems design mark is a trademark and service mark of Hitachi, Ltd. HiCommand is a registered trademark of Hitachi, Ltd.

Hitachi TagmaStore is a registered trademark of Hitachi Data Systems Corporation.

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All other brand or product names are or may be trademarks or service marks of and are used to identify products or services of their respective owners.

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iv Preface

Document Revision Level

Revision Date Description

MK-95RD277-P August 2005 Preliminary Release

MK-95RD277-00 September 2005 Initial Release

MK-95RD277-01 November 2005 Revision 1, supersedes and replaces MK-95RD227-00

MK-95RD277-02 February 2006 Revision 2, supersedes and replaces MK-95RD227-01

MK-95RD277-03 June 2006 Revision 3, supersedes and replaces MK-95RD227-02

Changes in this Revision

Added information about using external volumes as Pool volumes, see section 3.2

Added information about the V-VOL emulation type and capicity to section 3.3.1

Hitachi TagmaStore® USP and NSC Copy-on-Write Snapshot User’s Guide v

Preface

This document describes and provides instructions for using the Copy-on-Write Snapshot feature of the Hitachi TagmaStore® Universal Storage Platform (USP) and Network Storage Controller (NSC) storage subsystems.

This document assumes the following:

The user is familiar with the operating system and web browser software on the system hosting the Storage Navigator software.

The user has a background in data processing and understands RAID storage subsystems and their basic functions.

The user is familiar with the TagmaStore USP subsystem and has read and understands the User and Reference Guide for the subsystem and the Storage Navigator Users Guide (MK-94RD206).

Notes:

In this document the term “TagmaStore” refers to both the Universal Storage Platform and the Network Storage Controller, unless otherwise noted.

In this document the term “Universal Storage Platform (USP)” refers to all models of the TagmaStore USP subsystem, unless otherwise noted.

In this document the term “Network Storage Controller (NSC)” refers to all models of the TagmaStore NSC subsystem, unless otherwise noted.

This product includes software developed by the Apache Group for use in the Apache HTTP server project (http://www.apache.org/).

The Storage Navigator screens shown in this document were captured on a Windows® system with the Internet Explorer web browser. The Storage Navigator screens may display differently on other operating systems and browsers. For more information, see the Storage Navigator Users Guide (MK-94RD206).

Notice: The use of the Copy-on-Write Snapshot software and all other Hitachi Data Systems products is governed by the terms of your agreement(s) with Hitachi Data Systems.

Microcode Level

This document revision applies to TagmaStore USP/NSC microcode 50-07-5x and higher.

vi Preface

Convention for Storage Capacity Values

Storage capacity values for logical devices (LDEVs) on the TagmaStore USP and NSC are calculated based on the following values:

1 KB (kilobyte) = 1,024 bytes 1 MB (megabyte) = 1,0242 bytes 1 GB (gigabyte) = 1,0243 bytes 1 TB (terabyte) = 1,0244 bytes 1 block = 512 bytes

Referenced Documents

Hitachi TagmaStore Network Storage Controller:

– NSC User and Reference Guide (MK-95RD279)

Hitachi TagmaStore Universal Storage Platform:

– USP User and Reference Guide (MK-94RD231)

– ShadowImage for z/OS® User’s Guide (MK-94RD212)

– Command Control Interface User’s Guide (MK-90RD011)

Hitachi TagmaStore Universal Storage Platform and Network Storage Controller:

– Storage Navigator™ User’s Guide (MK-94RD206)

– Performance Manager User’s Guide (MK-94RD218)

– Universal Replicator User and Reference Guide (MK-94RD223)

– ShadowImage User Guide (MK-94RD204)

– LUN Manager User’s Guide (MK-94RD203)

– Cache Residency Manager User’s Guide (MK-94RD208)

– Virtual Partition Manager User’s Guide (MK-94RD259)

– Data Retention Utility User’s Guide (MK-94RD210)

– Universal Volume Manager User’s Guide.

Hitachi TagmaStore® USP and NSC Copy-on-Write Snapshot User’s Guide vii

Comments

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Fax: 858-695-1186

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Thank you! (All comments become the property of Hitachi Data Systems Corporation.)

Hitachi TagmaStore® USP and NSC Copy-on-Write Snapshot User’s Guide ix

Contents Chapter 1 Copy-on-Write Snapshot Overview.....................................................................................13

1.1 Copy-on-Write Snapshot Features ........................................................... 13 1.1.1 Copy-on-Write Snapshot and ShadowImage ....................................... 15

1.2 Copy-on-Write Snapshot Functionality ...................................................... 16 1.2.1 Copy-on-Write Snapshot General Use .............................................. 16

Chapter 2 Setting up Copy-on-Write Snapshot ...................................................................................17

2.1 Requirements for Using Copy-on-Write Snapshot ......................................... 17 2.1.1 Pool Volume Requirements .......................................................... 18 2.1.2 Primary Volume (P-VOL) Requirements............................................ 19 2.1.3 Virtual Volume (V-VOL) Requirements ............................................. 19

2.2 Calculating the Number of Snapshot Pairs to be Created................................ 20 2.2.1 Calculating Snapshot Pairs Using Differential Tables ............................ 20 2.2.2 Calculating Snapshot Pairs Using the Virtual Volume Management

Area Shared Memory Capacity....................................................... 22 2.2.3 Calculating the Number of Snapshot Pairs by Using the Number of

Pair Tables.............................................................................. 24 2.3 Combining Copy-on-Write Snapshot with Other Program Products..................... 25

2.3.1 Combining Copy-on-Write Snapshot with ShadowImage ........................ 26 2.3.2 Combining Copy-on-Write Snapshot with TrueCopy or Universal

Replicator............................................................................... 29 2.3.3 Combining Copy-on-Write Snapshot with Volume Migration.................... 31 2.3.4 Combining Copy-on-Write Snapshot with Data Retention Utility .............. 31

2.4 Installing and Uninstalling Copy-on-Write Snapshot ...................................... 31 2.4.1 Installing Copy-on-Write Snapshot.................................................. 32 2.4.2 Uninstalling Copy-on-Write Snapshot .............................................. 32

2.5 Copy-on-Write Snapshot Panel Information ................................................ 33 2.5.1 ShadowImage Main Panel ............................................................ 33

2.5.1.1 Volume List.................................................................. 35 2.5.2 The Pool Panel ......................................................................... 39

2.5.2.1 New Pool Panel ............................................................. 43 2.6 The V-VOL Panel ................................................................................ 44

2.6.1 S-Vol Path Information panel ........................................................ 47 2.6.2 New V-VOL Group Panel.............................................................. 49

2.6.2.1 Create V-VOL Wizard Panel (1) .......................................... 50 2.6.2.2 Create V-VOL Wizard Panel (2) .......................................... 52 2.6.2.3 Create V-VOL Wizard Panel (3) .......................................... 54

2.6.3 C.O.W. Snapshot tab of ShadowImage Main Panel ............................... 55 2.6.3.1 Preset List ................................................................... 58 2.6.3.2 Display Filter................................................................ 60 2.6.3.3 Pairsplit-S Panel ............................................................ 62

2.6.4 Detail Panel ............................................................................ 63

Chapter 3 Using Copy-on-Write Snapshot...........................................................................................65

3.1 Copy-on-Write Snapshot Overview........................................................... 65 3.1.1 Copy-on-Write Snapshot work flow................................................. 65

x Contents

3.1.2 Displaying the ShadowImage Main panel ........................................... 68 3.1.3 Creating the Virtual Volume Management Area................................... 69

3.1.3.1 Initializing the V-VOL Management Area................................ 69 3.1.3.2 Initializing the Pool Management Block ................................. 70

3.2 Creating and Deleting Pools ................................................................... 71 3.2.1 Creating the Pool ...................................................................... 71

3.2.1.1 Defining Pool capacity ..................................................... 71 3.2.2 Using External Volumes as Pool-VOLs............................................... 73 3.2.3 Creating New Pools .................................................................... 73 3.2.4 Changing Pool Information ........................................................... 77 3.2.5 Deleting Pools .......................................................................... 78

3.2.5.1 Deleting Individual Pools .................................................. 78 3.2.5.2 Deleting Multiple Pools .................................................... 78

3.3 Creating and Deleting Virtual Volumes ...................................................... 79 3.3.1 Creating New Virtual Volumes ....................................................... 79

3.4 Using LUSE to create a Virtual Volume ...................................................... 84 3.4.1 Deleting Virtual Volumes ............................................................. 85

3.5 Creating Copy-on-Write Snapshot Pairs...................................................... 86 3.6 Storing Snapshot Data .......................................................................... 88 3.7 Deleting Snapshot Data and Snapshot Pairs................................................. 89

3.7.1 Deleting Copy-on-Write Snapshot Pairs by Selecting the Pairs per Port ...... 90 3.7.2 Deleting Copy-on-Write Snapshot Pairs by Selecting the Pairs per Pool ...... 91

3.8 Restoring a Copy-on-Write Snapshot Pair ................................................... 93 3.8.1 Copy Threshold Option................................................................ 94

3.9 Copy-on-Write Snapshot Pair Status ......................................................... 95 3.9.1 Specifying the Volumes Displayed in the Volume List............................ 97

3.10 Displaying the Copy-on-Write Snapshot Pairs Detail Information ....................... 99 3.11 Displaying the Operation History ........................................................... 100

Chapter 4 Troubleshooting.................................................................................................................105

4.1 General Troubleshooting..................................................................... 105 4.2 Copy-on-Write Snapshot Troubleshooting ................................................. 106

4.2.1 Recovering a Blocked Pool.......................................................... 109 4.2.2 Completing Pool Related Service Information Messages (SIMs)............... 111 4.2.3 Switching Off the Power Supply ................................................... 112 4.2.4 Replacing the Microprogram Offline .............................................. 112

Acronyms and Abbreviations .................................................................................................................113

Hitachi TagmaStore® USP and NSC Copy-on-Write Snapshot User’s Guide xi

List of Figures Figure 1.1 Overview of Copy-on-Write Snapshot software functionality ..................... 14

Figure 2.1 ShadowImage Main Panel ............................................................... 33 Figure 2.2 Volume List................................................................................ 35 Figure 2.3 Pool Panel ................................................................................. 39 Figure 2.4 New Pool Panel ........................................................................... 43 Figure 2.5 V-VOL Panel ............................................................................... 44 Figure 2.6 S-Vol Path panel .......................................................................... 47 Figure 2.7 New V-VOL Group Panel................................................................. 49 Figure 2.8 Create V-VOL Wizard Panel (1)......................................................... 50 Figure 2.9 Create V-VOL Wizard Panel (2)......................................................... 52 Figure 2.10 Create V-VOL Wizard Panel (3)......................................................... 54 Figure 2.11 C.O.W. Snapshot Panel .................................................................. 55 Figure 2.12 Preset List ................................................................................. 58 Figure 2.13 Display Filter panel showing the Copy-on-Write Snapshot Tab ................... 60 Figure 2.14 Pairsplit-S panel .......................................................................... 62 Figure 2.15 Detail Panel for a Copy-on-Write Snapshot Pair..................................... 63

Figure 3.1 Procedure for Using Copy-on-Write Snapshot........................................ 66 Figure 3.2 ShadowImage Main panel ............................................................... 68 Figure 3.3 The Mechanism of Copy-on-Write Snapshot Pair and Pool......................... 71 Figure 3.14 Copy-on-Write Snapshot Pair Status Transitions .................................... 95 Figure 3.15 Copy-on-Write Snapshot Tab of the Display Filter Panel........................... 98 Figure 3.16 History Panel ............................................................................. 100

xii List of Tables

List of Tables Table 2.1 Copy-on-Write Snapshot Use Requirements .......................................... 17 Table 2.2 Pool-VOL Requirements.................................................................. 18 Table 2.3 P-VOL Requirements...................................................................... 19 Table 2.4 V-VOL Requirements ..................................................................... 19 Table 2.5 Volume Sharing with Other Program Products ....................................... 25 Table 2.6 Shared Copy-on-Write Snapshot P-VOL and ShadowImage P-VOL ................. 26 Table 2.7 Shared Copy-on-Write Snapshot P-VOL and ShadowImage S-VOL ................. 27 Table 2.8 ShadowImage Operations when Copy-on-Write Snapshot P-VOL and

ShadowImage P-VOL are Shared........................................................ 27 Table 2.9 ShadowImage Operations when Copy-on-Write Snapshot P-VOL and

ShadowImage S-VOL are Shared ........................................................ 28 Table 2.10 Copy-on-Write Snapshot Operations When Copy-on-Write Snapshot

P-VOL and TrueCopy / Universal Replicator P-VOL are Shared.................... 29 Table 2.11 Copy-on-Write Snapshot Operations When Copy-on-Write Snapshot

P-VOL and TrueCopy / Universal Replicator S-VOL are Shared.................... 29 Table 2.12 TrueCopy / Universal Replicator Operations When Copy-on-Write Snapshot

P-VOL and TrueCopy / Universal Replicator P-VOL are Shared.................... 30 Table 2.13 TrueCopy / Universal Replicator Operations When Copy-on-Write Snapshot

P-VOL and TrueCopy / Universal Replicator S-VOL are Shared.................... 30 Table 2.14 Information Displayed in Prog/Sync.................................................... 37 Table 2.15 Pop-up Menus of the Volume List ...................................................... 38 Table 2.16 Pop-up Menus of the Pool Tree ......................................................... 40 Table 2.17 Pop-up Menus of the V-VOL Group Tree............................................... 45 Table 2.18 Pop-up Menu of the Preset List in the ShadowImage Main Panel ................. 59

Table 3.1 Pair Statuses and the Results of the CCI Commands ................................ 87 Table 3.2 Whether Hosts can Access P-VOL and V-VOL ......................................... 97 Table 3.3 Copy-on-Write Snapshot History Reference Codes and Messages ............... 102

Table 4.1 Copy-on-Write Snapshot Troubleshooting........................................... 106

Hitachi TagmaStore® USP and NSC Copy-on-Write Snapshot User’s Guide 13

Chapter 1 Copy-on-Write Snapshot Overview

Hitachi Data Systems offers two internal mirroring solutions, Hitachi Copy-on-Write Snapshot software and Hitachi ShadowImage In-System Replication (ShadowImage). Copy-on-Write Snapshot is designed to reduce backup time and provide point-in-time backup copies. Copy-on-Write Snapshot accelerates backup and recovery processes by reducing the amount of disk storage, and by providing the capability for quick restoration of production data. This translates into the ability to blend high-availability solutions with advanced disaster recovery techniques so that recovery will happen almost automatically, whatever the reason for the failure, with no loss of data and no impact to the production environment.

The Copy-on-Write Snapshot program configuration includes a P-VOL, a number of V-VOLs, a data Pool (POOL), and the Command Control Interface (CCI, also known as HORKM, or RAID Manager).

1.1 Copy-on-Write Snapshot Features

Copy-on-Write Snapshot accelerates backup and recovery processes by reducing the amount of disk storage required and by providing the capability for quick restoration of production data. Copy-on-Write Snapshot builds Snapshots (point-in-time copies) and full-copy business continuance volumes of production data for non-disruptive backup. As a result, Copy-on-Write Snapshot reduces traditional, tape-based application restore time from hours to seconds.

Copy-on-Write Snapshot creates a volume pair from a primary volume (P-VOL), which contains the original data, and a virtual volume (V-VOL), which contains the snapshot data. Copy-on-Write Snapshot uses the V-VOL as the secondary volume (S-VOL) of the volume pair. Since each P-VOL is paired with its V-VOL independently, each volume can be maintained as an independent copy set.

Snapshot operations can be performed from a UNIX® and/or PC server host using the CCI software. Copy-on-Write Snapshot commands are issued from the CCI through the command device in the storage system.

14 Chapter 1 Copy-on-Write Snapshot Overview

Figure 1.1 Overview of Copy-on-Write Snapshot Software Functionality

In the figure above, Data A is stored on the P-VOL of a Copy-on-Write Snapshot pair. When the host requests to update Data A to Data B, Copy-on-Write Snapshot copies Data A to the Pool volume (Pool-VOL) before the P-VOL is updated with Data B. After Data A is copied to the Pool-VOL, Data B will be written to the P-VOL, and the P-VOL will be updated. You can access Data B in the P-VOL and Data A in the Pool-VOL from the S-VOL.


1.1.1 Copy-on-Write Snapshot and ShadowImage

Copy-on-Write Snapshot requires ShadowImage in order to function.

Copy-on-Write Snapshot and ShadowImage are similar as both program products create pairs. However, Copy-on-Write Snapshot uses V-VOLs as a secondary volume which reduces disk subsystem capacity requirements. Additionally, only the updated data of the P-VOL is copied to the V-VOL and the differential data is stored in the POOL. Therefore, the replicated volume created by Copy-on-Write Snapshot comprises differential data stored in the POOL and physical data from the primary volume (P-VOL). ShadowImage, which creates pairs from physical volumes, copies all of the data in the P-VOL to the S-VOL. This copy process requires more time but provides increased data security.

WARNING: Copy-on-Write Snapshot copies only the updated data in a P-VOL to the V-VOL. Therefore, data in the V-VOL is not guaranteed in the following cases.

– When physical failure occurs in a P-VOL

– When a Pool is blocked

In this document, terms are defined as follows:

Data Pool: volume in which only differential data is stored (Pool)

Snapshot Image: a virtual replica volume for the primary volume (V-VOL); this is an internal volume that is held for restoration purposes

16 Chapter 1 Copy-on-Write Snapshot Overview

1.2 Copy-on-Write Snapshot Functionality

Copy-on-Write Snapshot creates pairs consisting of a P-VOL and a V-VOL. When creating a pair, Copy-on-Write Snapshot uses the V-VOL as the secondary volume of the pair. In addition, the Snapshot data of the P-VOL can be managed by copying the data to the Pool.

1.2.1 Copy-on-Write Snapshot General Use

Use Storage Navigator to set up the Copy-on-Write Snapshot environment, and the P-VOLs, V-VOLs, and POOLs. Use CCI to provide remote operation and scripting capabilities. Storage Navigator and CCI allow you to perform Snapshot operations, such as Copy-on-Write Snapshot pair status information displays, defining the number of V-VOLs (snapshots) per P-VOL, and deleting Copy-on-Write Snapshot pairs. Instructions for paircreate and pairdelete, which are issued from the CCI, can be found in the Command Control Interface (CCI) Use’s Guide MK-90RD011-17


Chapter 2 Setting up Copy-on-Write Snapshot

In this chapter you’ll find the requirements for using Copy-on-Write Snapshot, the Pool, P-VOL, and V-VOL requirements, the calculations used to determine the number of pairs that Copy-on-Write Snapshot can create, its installation and un-installation procedures, and illustrations of the panels and dialog boxes, including their complete description, used in setting up and using Copy-on-Write Snapshot software. And finally, you’ll find information about combining Copy-on-Write Snapshot with other program products.

2.1 Requirements for Using Copy-on-Write Snapshot

This section describes the use requirements for Copy-on-Write, and the Pool, P-VOL, and V-VOL requirements,

Table 2.1 Copy-on-Write Snapshot Use Requirements

No. Item Requirement

1 RAID level RAID1, RAID5, or RAID6

2 Shared memory The shared memory for the differential table must be installed on the base board. The shared memory must be configured so that the V-VOL management area can be created in the shared memory. In addition, you must reserve at least 512 MB x 2 or as much as 2GB x 2 for the V-VOL management area on the option board.*

3 Prerequisite program product ShadowImage

4 Pool More than one Pool needs to be created. The maximum capacity of the Pool changes with the capacity of the shared memory.

5 V-VOL More than one V-VOL is required.

6 Operation Storage Navigator computer and Command Control Interface are required for the operation of Copy-on-Write Snapshot.

Note*: If you are using the TagmaStore Network Storage Controller you need to reserve 342MB × 2 capacity of the shared memory on the basic board because the Network Storage Controller does not have an option board.

18 Chapter 2 Setting up Copy-on-Write Snapshot

2.1.1 Pool Volume Requirements

Table 2.2 Pool-VOL Requirements


1 Volume type Logical volume (LDEV) You cannot specify the following volumes as Copy-on-Write Snapshot Pool-VOLs. LUSE volumes Volumes used by a pair or migration plan of another program product Volumes that are set Protect or Read Only attribute, or S-VOL Disable setting by

Data Retention Utility NAS volumes

2 Emulation type OPEN-V

3 Maximum number 131,072 However, the maximum number of Pool-VOLs that can be registered in each Pool is 1,024. In addition, the volume already registered as a Pool-VOL in a Pool cannot be registered in another Pool.

4 Path definition Not required. The volumes with path definition cannot be specified as a Pool-VOL

The capacity of a Pool is equal to the total capacity of the registered Pool-VOLs in the Pool. If the usage rate of the Pool exceeds its capacity, the status of the Copy-on-Write Snapshot pair changes to PSUE (status when failure occurred). If this happens, snapshot data cannot be stored in the Pool and the Copy-on-Write Snapshot pair must be deleted. To delete a Snapshot pair use pairsplit -s from the CCI, or the Pairsplit -S panel in StorageNavigator. For more details about deleting a Snapshot pair, see section 3.7.

When a Copy-on-Write Snapshot pair is deleted, the snapshot data stored in the Pool is deleted and the P-VOL and V-VOL relationship is released.


2.1.2 Primary Volume (P-VOL) Requirements

Table 2.3 P-VOL Requirements


1 Volume type Logical volume (LDEV) LUSE volume can be specified. Note: A LUSE P-VOL must be paired with a V-VOL of the same size and the same structure. For example, if a LUSE P-VOL is created by combining the volumes of 1GB and 2GB and 3GB in this order, you must specify the LUSE volume which has exactly the same size and the same combination order as the V-VOL. You cannot specify the following volumes as Copy-on-Write Snapshot P-VOLs Volumes used as Pool-VOLs V-VOLs of Copy-on-Write Snapshot pairs Volumes used by a Cross-System Copy pair NAS volumes


3 Maximum number 8,192 For details about the maximum number of Copy-on-Write Snapshot pairs that can be created, see section 2.2.

4 Path definition Required

5 Maximum capacity 2 TB

2.1.3 Virtual Volume (V-VOL) Requirements

Table 2.4 V-VOL Requirements


1 Volume type You cannot specify the following volumes as Copy-on-Write Snapshot V-VOLs. Volumes used by a pair or migration plan of another program product

Note: A LUSE V-VOL must be paired with a P-VOL of the same size and the same structure.


3 Maximum number 8,192 For details about the maximum number of Copy-on-Write Snapshot pairs that can be created, see section 2.2.

4 Path definition Required


2.2 Calculating the Number of Snapshot Pairs to be Created

The number of Copy-on-Write Snapshot pairs that can be created for a subsystem depends on the number of differential tables, the capacity of shared memory for the V-VOL management area, or the number of pair tables. Calculate the number of Copy-on-Write Snapshot pairs that can be created by first using the number of differential tables, and then by using the capacity of shared memory for V-VOL management area, and finally by using the number of pair tables. Compare the three results. The smallest value is the maximum number of Copy-on-Write Snapshot pairs that can be created for the subsystem.

The following sections describe the calculation methods used to determine the number of Copy-on-Write Snapshot pairs that can be created based on the number of differential tables, the capacity of shared memory for V-VOL management area, or the number of pair tables.

2.2.1 Calculating Snapshot Pairs Using Differential Tables

The subsystem can use a maximum of 13,652 differential tables, if additional shared memory is not installed, and 30,718 if additional shared memory is installed. To calculate the number of Copy-on-Write Snapshot pairs that can be created, calculate the number of differential tables required for the Copy-on-Write Snapshot pair and compare it with the number of differential tables of the whole subsystem. Other than Copy-on-Write Snapshot, the following program products use differential tables in TagmaStore™ USP.

– ShadowImage

– ShadowImage for z/OS®

– Compatible Mirroring for IBM FlashCopy®

– Compatible Mirroring for IBM FlashCopy® Version 2

– Cross-system Copy

– Volume Migration

If any of the abovementioned program products other than Copy-on-Write Snapshot are used in the same subsystem, the number of differential tables that can be used by Copy-on-Write Snapshot pairs is calculated by subtracting the number of differential tables used by the pairs (migration plan for Volume Migration) of the abovementioned program products from the number of differential tables of the whole subsystem.

Please refer to the manual of each program product for the calculation of the number of required differential tables for ShadowImage, ShadowImage for z/OS, Compatible Mirroring for IBM FlashCopy, Compatible Mirroring for IBM FlashCopy Version 2, Cross-system Copy, and Volume Migration.


To calculate the number of differential tables for each Copy-on-Write Snapshot pair, use the formula below: ((X) ÷ 256) ÷ (Z)

(X): Capacity of the volume (in kilobytes)

(Z): The number of slots that a differential table can manage (1,916 × 32) Note that you must round up the result of the calculation to the nearest whole number.

When the capacity of the volume ((X) in the formula above) is 16 GB (16,777,216 KB), the number of differential tables for each Copy-on-Write Snapshot pair can be calculated as follows. Example (16,777,216 ÷ 256) ÷ (1,916 × 32) = 1.06889

1.06889 will be 2 when the value after the decimal point is rounded up. This indicates that 2 differential tables are required to create a Copy-on-Write Snapshot pair.

Assume that no other program products use differential tables in a subsystem where additional shared memory is not installed. The number of differential tables that Copy-on-Write Snapshot can use is 13,652. To create Snapshot pairs that require 2 differential tables for each pair, the calculation will be as follows.

13,652 ÷ 2 = 6,826

Thus, the maximum number of Copy-on-Write Snapshot pairs that can be created is 6,826.


2.2.2 Calculating Snapshot Pairs Using the Virtual Volume Management Area Shared Memory Capacity

The V-VOL management area consists of the following 3 elements.

– Pool association information

– Pool management block

– Management information other than these above (shared memory is fixed to 8 MB)

To calculate the maximum number of Copy-on-Write Snapshot pairs that can be created for a subsystem, use the formula below: {((X) - 8) ÷ ((α) + (β))}

(X): Shared memory capacity for the whole V-VOL management area (in megabytes)

(α): Shared memory capacity for the Pool association information (in bytes)

(β): Shared memory capacity for the Pool management block (in bytes)

Note that you should round off the result of the calculation to the nearest whole number.

The calculation of the capacity of the shared memory of Pool association information (α) and the capacity of the shared memory of Pool management block (β) is described below.

Notes:

– You can check the capacity of the shared memory of Pool association information and Pool management block in the C.O.W. Snapshot panel. See Figure 3.13.

– If all the capacity of the V-VOL management area is used by Pool management block and Pool association information, the capacity ratio of the Pool management block and the Pool association information in the V-VOL management area will be fixed then. For details, see section 3.1.3.

(α)= ↑((Y) ÷ 256)↑ × 4 × 1.08 (β)= ↑((Z) ÷ 256)↑ × 32

(Y): Capacity of the Pool-VOL (in kilobytes)

(Z): Usage of the Pool (in kilobytes)

Note that you must round up the value enclosed by two upward arrows (↑) to the nearest whole number.


Note: Notes on calculating the usage of a Pool

– When copying snapshot data to the Pool, Copy-on-Write Snapshot always consumes a multiple of 256 KB of the capacity of the Pool.

– When snapshot data is stored consecutively, the capacity of the snapshot data and the usage of the Pool will be almost the same. However, the usage of the Pool may be larger than the capacity of the snapshot data in some cases, when snapshot data is stored at random.

When the shared memory capacity for the whole V-VOL management area ((X) in the formula above) is 2047 MB, the capacity of the Pool-VOL ((Y) in the formula above) is 16 GB (16,777,216 KB), and the usage of the Pool ((Z) in the formula above) is 1 GB (1,048,576 KB), the number of Copy-on-Write Snapshot pairs that can be created for a subsystem can be calculated as follows. Example (2047 - 8) ÷ [{(16,777,216 ÷ 256) × 4 × 1.08} + {(1,048,576 ÷ 256) × 32}] = 5162.02933...

According to the result above, the maximum number of Copy-on-Write Snapshot pairs that can be created is 5,162.


2.2.3 Calculating the Number of Snapshot Pairs by Using the Number of Pair Tables

Pair tables are used by Compatible Mirroring for IBM FlashCopy Version 2 and Copy-on-Write Snapshot pairs in order to store control information which is needed to manage the pairs. To create a Compatible Mirroring for IBM FlashCopy Version 2 pair or a Copy-on-Write Snapshot pair, you need one pair table for each pair.

Usually, up to 32,768 pair tables are available in one subsystem. However, if the relationship expansion function, which is the function of Compatible Mirroring for IBM FlashCopy Version 2, is effective, the maximum number of available pair tables in one subsystem will be 1,048,575.

Among the TagmaStore USP program products, only Compatible Mirroring for IBM FlashCopy Version 2 and Copy-on-Write Snapshot use pair tables. Therefore, if you use either of these applications, the number of available pair tables for Copy-on-Write Snapshot pairs can be calculated by subtracting the number of pair tables used by the Compatible Mirroring for IBM FlashCopy Version 2 pairs from the number of pair tables of the whole subsystem.

For information about how to check the number of pair tables used by Compatible Mirroring for IBM FlashCopy Version 2 pairs (i.e., the number of already created Compatible Mirroring for IBM FlashCopy Version 2 pairs), see the ShadowImage for z/OS User’s Guide.

For example, when the relationship expansion function is effective and the number of pair tables used by Compatible Mirroring for IBM FlashCopy Version 2 is 30,000, the number of Copy-on-Write Snapshot pairs that can be created for a subsystem can be calculated as follows. Example 32,768 – 30,000 = 2,768

According to the result above, 2,768 is the maximum number of Copy-on-Write Snapshot pairs that can be created.


2.3 Combining Copy-on-Write Snapshot with Other Program Products

Copy-on-Write Snapshot can create pairs by sharing volumes with other program products such as ShadowImage or TrueCopy. In addition, you can create Snapshot pairs by using volumes to which attributes are assigned by the Data Retention Utility or the CCI. The following table shows if Copy-on-Write Snapshot pairs can share volumes with other program products.

Some operations are restricted, according to the pair statuses, when Copy-on-Write Snapshot shares volumes with other program products, see Table 2.5 for additional information.

Table 2.5 Volume Sharing with Other Program Products

# Volumes of Other Program Products

Copy-on-Write Snapshot pair P-VOL

Copy-on-Write Snapshot pair V-VOL

1 ShadowImage pair P-VOL OK* No

2 ShadowImage pair S-VOL OK* No

3 TrueCopy pair P-VOL OK No

4 TrueCopy pair S-VOL OK No

5 Universal Replicator pair P-VOL OK No

6 Universal Replicator pair S-VOL OK No

7 Volume Migration source volume OK No

8 Volume Migration target volume No No

9 Read Only volume OK OK

10 Protect volume OK OK

11 “S-VOL Disable” volume OK OK

12 Volume with VMA No No

13 Volume with extents No No

14 Zero Read Capacity volume OK OK

15 Invisible volume OK OK

Note*: A ShadowImage pair and a Copy-on-Write Snapshot pair cannot have the same mirror unit (MU) number. For example, if the MU number of the ShadowImage pair is 0, you cannot create a Copy-on-Write Snapshot pair whose MU number is 0 and whose P-VOL is also used as a ShadowImage P-VOL. Also, if the MU number of the Copy-on-Write Snapshot pair is 1, you cannot create a ShadowImage pair whose MU number is 1 and whose P-VOL is also used as a Copy-on-Write Snapshot P-VOL.


Notes:

– You need the Data Retention Utility to set the read only attribute, protect attribute, S-VOL Disable, or VMA. For details, please refer to Data Retention Utility User’s Guide.

– You need the CCI to set extents Zero Read Capacity attribute, or Invisible attribute. For details, please refer to Command Control Interface (CCI) User and Reference Guide.

– You can check if the volume has the read only attribute, protect attribute, S-VOL Disable, VMA, extents Zero Read Capacity attribute, or the invisible attribute by looking at the Data Retention Utility panel.

2.3.1 Combining Copy-on-Write Snapshot with ShadowImage

When a Copy-on-Write Snapshot P-VOL and a paired ShadowImage volume are shared, the relationship between the ShadowImage pair status and Copy-on-Write Snapshot operations are shown in Table 2.6 and Table 2.7.

Table 2.6 Shared Copy-on-Write Snapshot P-VOL and ShadowImage P-VOL

ShadowImage Pair Status No. Copy-on-Write Snapshot Operations

COPY PAIR COPY (SP)

PSUS (SP)

PSUS COPY (RS)

COPY (RS-R)

PSUE

1 Creating pairs (paircreate) OK OK OK OK OK OK No OK

2 Storing snapshot data (pairsplit)

OK OK OK OK OK OK No OK

3 Restoring pairs (pairresync –restore)

No No No No OK No No OK

4 Deleting snapshot data (pairresync)

OK OK OK OK OK OK OK OK

5 Deleting pairs (pairsplit –S) OK OK OK OK OK OK OK OK


Table 2.7 Shared Copy-on-Write Snapshot P-VOL and ShadowImage S-VOL

ShadowImage Pair Status No. Copy-on-Write Snapshot Operations

COPY PAIR COPY (SP)

PSUS (SP)

PSUS COPY (RS)

COPY (RS-R)

PSUE

1 Creating pairs (paircreate)

No No No No OK No No No







5 Deleting pairs (pairsplit –S)


The relationship between the Copy-on-Write Snapshot pair status and ShadowImage operations are shown in Table 2.8 and Table 2.9.

Table 2.8 ShadowImage Operations when Copy-on-Write Snapshot P-VOL and ShadowImage P-VOL are Shared

Copy-on-Write Snapshot Pair Status No. ShadowImage Operations

COPY PAIR PSUS SMPL (PD)

COPY (RS)

COPY (RS-R)

PSUE


OK OK OK OK OK No OK

2 Creating and splitting pairs (paircreate –split)


3 Splitting pairs (pairsplit) OK OK OK OK OK No OK

4 Forward pair resynchronization (pairresync)


5 Normal backward pair resynchronization (pairresync –restore)


6 Quick backward pair resynchronization (pairresync –restore)

No No No No No No No

7 Suspending pairs (pairsplit –E)

OK OK OK OK OK OK OK




Table 2.9 ShadowImage Operations when Copy-on-Write Snapshot P-VOL and ShadowImage S-VOL are Shared

Copy-on-Write Snapshot Pair Status No. ShadowImage Operations


COPY (RS)

COPY (RS-R)

PSUE



2 Creating and splitting pairs (paircreate –split)


3 Splitting pairs (pairsplit) OK OK OK OK OK No OK

4 Forward pair resynchronization (pairresync)


5 Normal backward pair resynchronization (pairresync –restore)


6 Quick backward pair resynchronization (pairresync –restore)


7 Suspending pairs (pairsplit –E)




Note: Since a Copy-on-Write Snapshot V-VOL uses the data in the P-VOL, ShadowImage’s quick backward pairresync operation (Quick Restore) is not allowed.


2.3.2 Combining Copy-on-Write Snapshot with TrueCopy or Universal Replicator

When the Copy-on-Write Snapshot P-VOL and the volume of TrueCopy or Universal Replicator pair are shared, the relationship between the TrueCopy or Universal Replicator pair status and Copy-on-Write Snapshot operations is to be as shown in Table 2.10 and Table 2.11.

Table 2.10 Copy-on-Write Snapshot Operations When Copy-on-Write Snapshot P-VOL and TrueCopy / Universal Replicator P-VOL are Shared

TrueCopy / Universal Replicator Pair Status No. Copy-on-Write Snapshot Operations

COPY PAIR PSUS PSUE Suspending Deleting

1 Creating pairs (paircreate) OK OK OK OK OK OK


OK OK OK OK OK OK


No No OK OK No No


OK OK OK OK OK OK


OK OK OK OK OK OK

Table 2.11 Copy-on-Write Snapshot Operations When Copy-on-Write Snapshot P-VOL and TrueCopy / Universal Replicator S-VOL are Shared

TrueCopy / Universal Replicator Pair Status No. Copy-on-Write Snapshot Operations COPY PAIR PSUS PSUE SSWS*1 Suspending Deleting




No OK OK OK OK OK OK

3 Restoring pairs (pairresync –restore) *2






Note*1: SSWS is a status of Universal Replicator pairs. TrueCopy pairs will not change to SSWS status.

Note*2: When you restore the Copy-on-Write Snapshot pair whose P-VOL is used as a TrueCopy or Universal Replicator S-VOL, you need to switch operations from the local site to the remote site by executing the horctakeover command.


The relationship between the Copy-on-Write Snapshot pair status and TrueCopy or Universal Replicator operations is to be as shown in Table 2.12 and Table 2.13.

Table 2.12 TrueCopy / Universal Replicator Operations When Copy-on-Write Snapshot P-VOL and TrueCopy / Universal Replicator P-VOL are Shared

Copy-on-Write Snapshot Pair Status No. TrueCopy / Universal Replicator Operations


COPY (RS)

COPY (RS-R)

PSUE

1 Creating pairs (paircreate) OK OK OK OK OK No OK

2 Splitting pairs (pairsplit) OK OK OK OK OK — OK

3 Resynchronizing pairs (pairresync)


4 Deleting pairs (pairsplit –S) OK OK OK OK OK OK OK

5 Switching to remote site (horctakeover)


Table 2.13 TrueCopy / Universal Replicator Operations When Copy-on-Write Snapshot P-VOL and TrueCopy / Universal Replicator S-VOL are Shared

Copy-on-Write Snapshot Pair Status No. TrueCopy / Universal Replicator Operations


COPY (RS)

COPY (RS-R)

PSUE

1 Creating pairs (paircreate) No No No OK No No No

2 Splitting pairs (pairsplit) OK OK OK OK OK OK OK

3 Resynchronizing pairs (pairresync)




5 Switching to remote site (horctakeover)


For detailed information about TrueCopy pair status and operations, please refer to the TrueCopy User’s Guide. For detailed information about Universal Replicator pair status and operations, please refer to the Universal Replicator User’s Guide.


2.3.3 Combining Copy-on-Write Snapshot with Volume Migration

Regardless of the status of the migration plans of Volume Migration (Volume Migration pairs), you cannot perform any Copy-on-Write Snapshot operations on the volume that is used by the migration plan. In order to use a Copy-on-Write Snapshot P-VOL as the source volume of the migration plan, you need to create the Copy-on-Write Snapshot pair first, then create the migration plan.

When Copy-on-Write Snapshot P-VOL and the source volume of the migration plan are shared, you can execute the migration plan only when the Copy-on-Write Snapshot pair is in PAIR status. Deleting and canceling the migration plan are always allowed. These operations are not affected by the Copy-on-Write Snapshot pair status.

For detailed information about the status of the migration plan and Volume Migration operations, please refer to the Performance Manager User’s Guide.

2.3.4 Combining Copy-on-Write Snapshot with Data Retention Utility

Data Retention Utility can set four different kinds of access attributes on the volumes; Read/Write, Read Only, Protect, and S-VOL Disable. Copy-on-Write Snapshot cannot create a pair by specifying the volume whose access attribute is S-VOL Disable as the S-VOL. In addition, if the S-VOL Disable attribute is set on the P-VOL of the Copy-on-Write Snapshot pair, you cannot restore the pair.

By using Data Retention Utility, you may set read/write, read only, protect, or S-VOL Disable attribute on the volumes that are already used by the Copy-on-Write Snapshot pairs. However, when the pair is in the following status, you cannot set the S-VOL Disable attribute on the pair volumes.

– COPY*

– SMPL(PD)*

– COPY(RS)*

– COPY(RS-R)

– PSUE*

Note*: You may set S-VOL Disable on the P-VOL even if the pair status is COPY, SMPL(PD), COPY(RS), or PSUE.

For detailed information about setting the access attribute, please refer to the Data Retention Utility User’s Guide.

2.4 Installing and Uninstalling Copy-on-Write Snapshot

Before installing Copy-on-Write Snapshot, review the shared memory requirements for the differential tables and the V-VOL management area.

Note: Please call the Support Center to install additional shared memory for the V-VOL management area.


2.4.1 Installing Copy-on-Write Snapshot

1. If not already installed, please install shared memory for differential tables.

2. Install additional shared memory for the V-VOL management area.

When you’re using the TagmaStore Network Storage Controller, you do not need to install additional shared memory. You only need to define the shared memory for V-VOL management area.

3. Install ShadowImage if its not already installed. ShadowImage provides essential functionality for Copy-on-Write Snapshot and is a required component.

4. Install Copy-on-Write Snapshot.

Note:

– You cannot partially uninstall shared memory in the V-VOL management area. Once you install additional shared memory for the V-VOL management area, you cannot partially uninstall it. You must uninstall all of the shared memory that was added for the V-VOL management area.

– The shared memory and ShadowImage can be installed in any order.

2.4.2 Uninstalling Copy-on-Write Snapshot

On occasion it may be necessary to uninstall Copy-on-Write Snapshot.

1. Delete all Copy-on-Write Snapshot pairs.

2. Delete all Pools.

3. Delete all V-VOLs.

4. Uninstall Copy-on-Write Snapshot.

For detailed information about the procedures for deleting the pairs, Pools, and V-VOLs, see Chapter 3.


2.5 Copy-on-Write Snapshot Panel Information

This section provides illustrations of the panels used in Copy-on-Write Snapshot operation and includes descriptions for all of the functions within each panel.

2.5.1 ShadowImage Main Panel

The ShadowImage Main panel is used to access the Copy-on-Write Snapshot panels, and is used to control several of its features.

Figure 2.1 ShadowImage Main Panel

Note: Though the ShadowImage Main panel displays information about both ShadowImage and Copy-on-Write Snapshot pairs, this section only explains the items related to the Copy-on-Write Snapshot pairs. For details about the items related to the ShadowImage pairs, please refer to the ShadowImage User’s Guide.


The ShadowImage Main panel displays the following items.

Display Filter button

Displays the Display Filter panel (Figure 2.13) where you can filter the volumes displayed in the volume list.

Tree (i.e. the area in the left of the panel)

Displays the ports that are defined paths, host groups, iSCSI targets, or LUNs in tree style. When you select the items in the tree, information about ShadowImage pairs or Copy-on-Write Snapshot pairs will be displayed in the volume list on the right of panel.

If you want to display information about all the pairs in the disk subsystem, select Subsystem which is shown in the top of the tree.

The following icons are displayed in the tree.

– : disk subsystem

– : port

– : host group, or iSCSI target

– : LUN

Volume list (i.e. the area in the upper right of the panel)

Displays ShadowImage pairs or Copy-on-Write Snapshot pairs on the port, host group, iSCSI target, or LUN that you selected in the tree. You can sort the volumes by any of the items displayed as the column header of the volume list.

Preset list

Displays the operations that have been performed in the ShadowImage Main panel, but have not been applied to the USP subsystem. Select the Apply button to apply the operations displayed in the Preset list to the USP subsystem.

For details about the items displayed in the Preset list, see section

Apply button

Applies the operations displayed in the Preset list to the TagmaStore USP subsystem. If the specified operations are applied successfully, the Preset list will be cleared. If an error occurs during an operation, the failed operation will remain in the Preset list with an error icon ( ) displayed in front. Details of the error (error code and message) are displayed on the error panel. For details about the list of the error code of Copy-on-Write Snapshot, please refer to the Storage Navigator™Error Codes.

Cancel button

Cancels all the operations set in the Preset list.


2.5.1.1 Volume List

The volume list is the upper right area in the ShadowImage Main panel. The volume list displays the volumes that can be used by the ShadowImage or the Copy-on-Write Snapshot and the pair information about these two products.

Figure 2.2 Volume List

When you select a port, host group, iSCSI target, or LUN in the tree on the left side of the ShadowImage Main panel, information about the volumes that belong to what you selected in the tree will be displayed in the volume list. You can specify the conditions such as pair status or reserved attribute on the Display Filter panel in order to select the volumes that are allowed to be displayed in the volume list. For the information about the use of the Display Filter panel, see section 2.6.3.2.


The volume list displays the following items.

Previous button

When the total number of the volumes in the disk subsystem is more than 1,024, the Previous button displays the previous page of the volume list. If the number of the items in the volume list is less than 1,024, this button is grayed out.

Next button

When the total number of the volumes in the disk subsystem is more than 1,024, the Next button displays the next page of the volume list. If the number of the items in the volume list is less than 1,024, this button is grayed out.

Port

The port ID (cluster and channel number) of the P-VOL is displayed.

G-ID

The group number of the host group or iSCSI target of the P-VOL is displayed.

LUN

The CU:LDEV (control unit image:logical device ID) of the P-VOL is displayed.

Note: An LDEV number that ends with a “#” mark indicates that the LDEV is an external volume (e.g. 00:01#). For details regarding the external volumes, please refer to the Universal Volume Manager User’s Guide.

MU

The snapshot ID of a Copy-on-Write Snapshot pair will be displayed. If the pair is in SMPL status, three continue hyphens (---) will be displayed. For details about what will be displayed in this item if you select ShadowImage pairs, please refer to the ShadowImage User’s Guide.

Status

The status of a Copy-on-Write Snapshot pair or a ShadowImage pair is displayed. For details about the status of a Copy-on-Write Snapshot pair, see section 3.1. For details about the ShadowImage pair status, please refer to the ShadowImage User’s Guide.

Port

The port ID (cluster and channel number) of the S-VOL is displayed. If there is no S-VOL, --- is displayed.

G-ID

The group number of the host group or iSCSI target of the S-VOL is displayed. If there is no S-VOL, --- is displayed.

LUN(S)

The CU:LDEV (control unit image:logical device ID) of the S-VOL is displayed. If there is no S-VOL, --- is displayed.

Note: An LDEV number that ends with a “V” mark indicates that the LDEV is an virtual volume (e.g. 00:01 V).


CTG

--- is displayed. For information about what will be displayed if it is a ShadowImage pair, please refer to the ShadowImage User’s Guide.

SvolMode

The S-VOL status is displayed. When the data is not written in the S-VOL, --- is displayed. When the data is written in the S-VOL, W is displayed. For information about what will be displayed for a ShadowImage pair, please refer to the ShadowImage User’s Guide.

Pace


Prog./Sync.

Displays the consistency rate of the P-VOL and the S-VOL of the Snapshot pair. The displayed Information changes according to the pair status. See the following table.

Table 2.14 Information Displayed in Prog/Sync

Pair Status Displayed Information

SMPL --- is displayed.

COPY

PAIR

COPY(RS)

COPY(RS-R)

PSUS

The consistency rate of the P-VOL and the S-VOL is displayed by percent (%).

PSUE

SMPL(PD)

--- is displayed.

For information about what will be displayed when a ShadowImage pair is shown, please refer to the ShadowImage User’s Guide.

Type

The emulation type of the volume is displayed.

Capacity(MB)

The storage capacity of the volume is displayed. The unit is megabyte (MB).

CLPR(P)

The cache logical partition of the P-VOL is displayed.

CLPR(S)

The cache logical partition of the S-VOL is displayed.


Pop-up menu

When you select the Copy-on-Write Snapshot pair volumes in the volume list and right-click them, the pop-up menus in Table 2.15 will be displayed.

Table 2.15 Pop-up Menus of the Volume List

Command Function

Detail Opens the Detail panel (Figure 2.15).

Pairsplit-S Opens the Pairsplit-S panel (Figure 3.12).

S-Vol Path Opens the S-Vol Path panel (Figure 2.6).

Display Filter Opens the Display Filter panel (Figure 2.13).

Note:

– The grayed out commands are for ShadowImage pairs. For details about those commands, please refer to the ShadowImage User’s Guide.

– When you select Paircreate or Pairsplit from the pop-up menu, the Paircreate panel or the Pairsplit panel will be displayed. However, you cannot create or split Copy-on-Write Snapshot pairs by using these panels.

Volumes X

X indicates the total number of the volumes in the disk subsystem.

Pairs W(X)/Y/Z

W indicates the total number of ShadowImage pairs.

X indicates the total number of the ShadowImage pairs and ShadowImage for z/OS pairs.

Y indicates the total number of the Copy-on-Write Snapshot pairs.

Z indicates the maximum number of pairs (ShadowImage/ Copy-on-Write Snapshot/ ShadowImage for z/OS/ Volume Migration/ Cross-System Copy/ Compatible Mirroring for IBM FlashCopy/ Compatible Mirroring for IBM FlashCopy Version 2) that can be created in one disk subsystem.

Note: The number of Copy-on-Write Snapshot pairs that can be created in one disk subsystem depends on the number of differential tables or the capacity of shared memory for V-VOL management area. For details, see section 2.2.

Reserved X(Y)/Z

Information about the number of reserved volumes of the ShadowImage pairs is displayed. For details about this item, please refer to the ShadowImage User’s Guide.


2.5.2 The Pool Panel

Figure 2.3 Pool Panel

You can also initialize the V-VOL management area or the Pool management block by using the Pool panel. For details, see section 3.1.3.

The Pool panel displays these items.

Pool Mng. Block used capacity: X GB

X indicates the capacity of the Pool management blocks in use.

Caution: The value displayed at the Total Capacity of the Pool Information box and the value displayed at the Pool Mng. Block used capacity are approximately equal, but there may be some difference. Even if the value displayed at the Total Capacity of the Pool Information box is updated when the Pool-VOLs are added to or deleted from the Pool, the value displayed at the Pool Mng. Block used capacity will not be updated until you select the Apply button.

Pool Mng. Block total capacity: X GB

X indicates the total capacity of the Pool management blocks, including the capacity of the blocks in use.

Note: You need to keep the capacity of the Pool management blocks in use less than its total capacity.


Pool tree

Pools in the disk subsystem are displayed in the tree style. The icons below indicate Pool status.

– : The disk subsystem or Copy-on-Write Snapshot

– Pool (ID): a Pool in normal status

– Pool (ID): the Pool usage rate exceeds the threshold value

– Pool (ID): a blocked Pool

– : a normal Pool (in the process of deleting)

– : a blocked Pool (in the process of deleting)

Pop-up menu

When you select the icons in the Pool tree and right-click them, the pop-up menus in Table 2.16 will be displayed.

Table 2.16 Pop-up Menus of the Pool Tree

Menu Function

New Pool Opens the New Pool panel (Figure 2.4). You can select this pop-up menu only when you right clicked the C.O.W. Snapshot icon

Delete Pool(s) Deletes multiple Pools at a time. You can select this pop-up menu only when the Pools that can be deleted exist

When you right click the C.O.W. Snapshot icon

Restore Pool(s) Recover multiple blocked Pools to the normal status at a time. You can select this pop-up menu only when the blocked Pools exist

Change Pool Information

Opens the Change Pool Information panel (Figure 3.6).

Delete Pool Deletes the Pool

When you right-click the Pool icon

Restore Pool Recover the blocked Pool to the normal status. You can select this pop-up menu only when you right clicked the blocked Pool icon

Pool-VOL list

Information about the Pool-VOLs that are registered in the Pool selected in the Pool tree. The following items are displayed in the list.

– CU:LDEV: CU number and LDEV number of the Pool-VOL

Note: An LDEV number that ends with a hash (#) mark indicates that the LDEV is an external volume (e.g. 00:01#). For details regarding the external volumes, please refer to the Universal Volume Manager User’s Guide.

– Capacity: capacity of the Pool-VOL

– Emulation: emulation type of the Pool-VOL

– PG: parity group to which the Pool-VOL belongs

– Total Capacity: total capacity of the Pool-VOLs in the Pool

– Used LDEVs: total number of the Pool-VOLs in the Pool

– Remaining LDEVs: total number of the Pool-VOLs that you can add to the Pool


Add Pool-VOL button

Adds the selected volume(s) in the Free LDEVs list as Pool-VOL(s) to the Pool that you selected from the Pool tree.

CU dropdown list

If you select a CU number from the dropdown list, the volumes in the CU will be displayed in the Free LDEVs list.

Free LDEVs list

Among the volumes in the CU which is selected from the CU dropdown list, the volumes that can be specified as Pool-VOLs will be displayed. The following items are displayed in the list.

– CU:LDEV: CU number and LDEV number of the volume

Note: An LDEV number that ends with a hash (#) mark indicates that the LDEV is an external volume (e.g. 00:01#). For details regarding the external volumes, please refer to the Universal Volume Manager User’s Guide.

– Capacity: capacity of the volume

– Emulation: emulation type of the volume

– PG: parity group to which the volume belongs

– CLPR: CLPR number of the CLPR to which the volume belongs

– Selected LDEVs: total number of the volumes that are selected in the list

Pool Information box

Information about the Pool that you selected in the Pool tree will be displayed. The following items are displayed in the box.

– Pool ID: number that identifies the Pool

– Status: status of the Pool

– Normal: Pool is in the normal status

– Warning: usage rate of the Pool exceeds the threshold

– Blocked: Pool is blocked

– Total Capacity: total capacity of the Pool

– Used Capacity: used capacity of the Pool

– Usage Rate: proportion of the used Pool capacity to the total Pool capacity (%) If the usage rate exceeds the threshold, Warning will be displayed after the usage rate. If the usage rate reaches 100 %, Error will be displayed after the usage rate.

– Threshold: threshold for Pool usage rate (%)

– Attribute: program product that uses the Pool

– C.O.W. Snapshot: Copy-on-Write Snapshot

– CLPR: CLPR number of the CLPR to which the Pool belongs


Initialize button

If there is no Pool in the disk subsystem, this button initializes the entire V-VOL management area. If Pools exist in the disk subsystem, this button initializes the Pool management block in the V-VOL management area. The Pool management block needs up to 20 minutes to complete initialization.

If you click this button, all the operations which are performed in the Pool panel before then but not yet applied to the disk subsystem will be canceled.

SIM Complete Request check box

Completes the SIMs related to Pools. If you select the check box and click the Apply button, the SIMs that occurred when the usage rate of a Pool exceeds the threshold, or when a Pool becomes blocked will be cleared. For details about SIM complete, see section 4.2.2.

Apply button

Applies the operations that are performed in the Pool panel to the disk subsystem. If the specified operations complete successfully, the contents that were displayed in the blue-italic fonts in the Pool tree or Pool-VOL list change to normal black fonts.

If an error occurs during the operations, the error code and error message will be displayed in the error message panel. For details about the list of the error code of Copy-on-Write Snapshot, please refer to the Storage Navigator™Error Codes.

Cancel button

Cancels all operations performed in the Pool panel.


2.5.2.1 New Pool Panel

Figure 2.4 New Pool Panel

The New Pool panel displays the following items.

Pool ID text box

Enter the Pool ID in the text box in whole numbers between 0 and 127.

Note: Do not enter and Set a Pool ID that is already in use. Doing so will generate an error message.

Threshold dropdown list

You can select the threshold of the Pool usage rate between 20 and 95.

Note: Unit of the threshold is percent ( % ). If the Pool usage rate exceeds the threshold, the Pool status changes to Warning. You cannot create new Copy-on-Write Snapshot pairs to the Pool in Warning status. Be careful not to set too small value for the threshold.

Attribute dropdown list

You can select the program product that uses the Pool.

Set button

Creates a new Pool according to the settings in the New Pool panel and closes the panel.

Cancel button

Cancels the settings in the New Pool panel and closes the panel. No Pool will be created.


2.6 The V-VOL Panel

To display the V-VOL panel:

1. Start Storage Navigator and display the Storage Navigator main panel.

2. Select the LUN Expansion (LUSE) / Virtual LVI/LUN (VLL) start button.

The LUN Expansion panel is displayed.

3. Select the V-VOL tab.

Figure 2.5 V-VOL Panel

Note: In the V-VOL panel, you create or delete the V-VOLs per a V-VOL group. If you want to create or delete a V-VOL by itself, use the Virtual LVI/LUN function. For details about the Virtual LVI/LUN function, please refer to the LUN Expansion/ Virtual LVI/LUN User’s Guide.


The V-VOL panel displays the following items.

V-VOL group tree (i.e. the area in the left of the panel)

The V-VOL groups in the disk subsystem are displayed in the tree style. The following icons are displayed in the tree.

– : The disk subsystem

– : V-VOL group

– : V-VOL group (in the process of deleting)

– : VDEV

Pop-up menu

When you select the icons in the V-VOL group tree and right-click them, the pop-up menus in Table 2.17 will be displayed.

Table 2.17 Pop-up Menus of the V-VOL Group Tree

Command Function

New V-VOL Group Opens the New V-VOL Group panel (Figure 3.7). You can select this command only when you right clicked the Subsystem icon.

Delete V-VOL Group Deletes the V-VOL group and the V-VOLs that are in that V-VOL group. You can select this command only when you right clicked the V-VOL group icon.

V-VOL list (i.e. the area in the right of the panel)

Information about the V-VOLs that are registered in the VDEV selected in the V-VOL group tree. The following items are displayed in the list.

– CU:LDEV: CU number and LDEV number of the V-VOL

– Capacity: capacity of the V-VOL

– Emulation: emulation type of the V-VOL

Note: If the emulation type is followed by CVS, the volume is a CV(customized volume). For details about CV, please refer to the LUN Expansion and Virtual LVI/LUN User's Guide.

– Status: status of the V-VOL

– Normal

– Blocked

– CLPR: CLPR number of the CLPR to which the V-VOL belongs

– Access Attribute: access attribute of the V-VOL

– Path: LU path of the V-VOL


Apply button

Applies the operations that are performed in the V-VOL panel to the disk subsystem. If the specified operations complete successfully, the contents that were displayed in the blue-italic fonts in the V-VOL group tree or V-VOL list change to normal black fonts.

If an error occurs during the operations, the error code and error message will be displayed in the error message panel. For details about the list of the error code of Copy-on-Write Snapshot, please refer to the Storage Navigator™Error Codes.

Cancel button

Cancels all the operations that are performed in the V-VOL panel.


2.6.1 S-Vol Path Information panel

To display the S-Vol Path panel:

1. Display the ShadowImage Main panel.

2. Select and right-click a Copy-on-Write Snapshot pair on the volume list.

A pop-up menu is displayed.

3. Select S-Vol Path from the menu.

The S-Vol Path panel is displayed.

Figure 2.6 S-Vol Path panel


S-Vol Path panel displays the following items.

Pair Information box

The following information items of the Copy-on-Write Snapshot pair is displayed.

– Port(P): port ID of the P-VOL

– G-ID(P): the group number of host group or iSCSI target of the P-VOL

– LUN(P): LUN of the P-VOL

– Port(S): port ID of the S-VOL

– G-ID(S): the group number of host group or iSCSI target of the S-VOL

– LUN(S): LUN of the S-VOL

S-Vol Path Information box

The S-VOL path information of the Copy-on-Write Snapshot pair is selected in the Pair Information box.

– Port: port ID of the S-VOL

– G-ID: the group number of host group or iSCSI target of the S-VOL

– LUN: LUN of the S-VOL

OK button

Closes the S-Vol Path panel.


2.6.2 New V-VOL Group Panel

Figure 2.7 New V-VOL Group Panel

New V-VOL Group panel displays these items.

V-VOL Group dropdown list

You can either select or enter the V-VOL group ID in the dropdown list. The whole number from 1 to 8192 can be either selected or entered in the dropdown list.

Note: Do not enter the V-VOL group ID that is already used by another V-VOL group. If you enter the V-VOL group ID that is already used by another V-VOL group and select the Next button, an error message will be displayed. In that case, please either select or enter a different number for the new V-VOL group ID.

Emulation Type dropdown list

You can select the emulation type of the V-VOL group.

CLPR dropdown list

You can select the CLPR of the V-VOL group.

Next button

Fixes the settings in the New V-VOL Group panel and displays the Create V-VOL wizard panel (1).

Cancel button

Cancels the settings in the New V-VOL Group panel and closes the panel.


2.6.2.1 Create V-VOL Wizard Panel (1)

Figure 2.8 Create V-VOL Wizard Panel (1)


The Create V-VOL wizard panel (1) displays the following items.

V-VOL Group

V-VOL group ID that you set in the New V-VOL Group panel is displayed.

Emulation Type dropdown list

You can select the emulation type of the V-VOL.

Capacity Unit dropdown list

You can select the unit of the capacity of the V-VOL. MB (megabyte), block, or Cyl.

Capacity text box

You can enter the capacity of the V-VOL in the text box. If you selected MB from the Capacity Unit dropdown list, you can enter the whole number from 46 to 2097151. If you selected block from the dropdown list, you can enter the whole number from 96000 to 4294967296. If you selected Cyl from the Capacity Unit dropdown list, you can enter the whole number from 50 to 2236962.

Number of V-VOL text box

You can enter the number of the V-VOLs that you want to add in the text box. Enter the whole number from 1 to 256.

Set button

Adds the V-VOL(s) to the V-VOL information setting list.

Delete button

Deletes the selected V-VOL(s) from the V-VOL information setting list.

V-VOL information setting list (i.e. middle of the panel)

Information about the V-VOL(s) that you are going to create is displayed.

– No.: number



Back button

Returns to the New V-VOL Group panel while maintaining the settings in this panel.

Next button

Confirms the setting in this panel and moves to the Create V-VOL wizard panel (2).

Cancel button

Cancels the setting in the Create V-VOL wizard panel (1) and closes the panel.



V-VOL Group

V-VOL group ID is displayed.

V-VOL information setting list (i.e. upper right area of the panel)


– No.: number



Select CU No. dropdown list

You can select the CU number.

Interval dropdown list

You can select the interval between the LDEV numbers that need to be assigned to the newly created V-VOLs. If you select 0, the LDEV numbers will be sequential.

Note:

– The value you specify as the interval between LDEV numbers counts only the available LDEV numbers and skips those that are not selectable.

– Even when you use the multiple CUs, LDEV numbers will be assigned according to the setting in the Interval dropdown list.

Select LDEV No. area

The settings of LDEV numbers for the CU number selected from the Select CU No. dropdown list are displayed. Numbers in the upper end and the left side indicate the LDEV number. For example, the LDEV number of the cell whose upper end is +2 and the left side is +10 is 12.

Gray cells indicate the LDEV numbers that are already used for other volumes, white cells indicate the unused LDEV numbers, and blue cells indicate the LDEV numbers that are selected for the V-VOLs in this panel.

CU number of another SLPR is used. check box

Allows you to select the CU numbers of the SLPR other than the SLPR now you are in.

Back button

Returns to the Create V-VOL wizard panel (1) while maintaining the settings in this panel.

Next button

Fixes the setting in this panel and moves to the Create V-VOL wizard panel (3).

Cancel button






V-VOL information setting list (i.e. middle of the panel)


– VDEV: VDEV number



– CU:LDEV: CU number and LDEV number of the V-VOL

Back button

Returns to the Create V-VOL wizard panel (2) while maintaining the settings in this panel.

OK button

Fixes the setting in the Create V-VOL wizard panel (3) and closes the panel.

Cancel button



2.6.3 C.O.W. Snapshot tab of ShadowImage Main Panel

Figure 2.11 C.O.W. Snapshot Panel

The C.O.W. Snapshot panel displays the following items.

Tree (i.e. the area in the left of the panel)

Pools in the disk subsystem are displayed in the tree style. The following icons are displayed in the tree.

– : disk subsystem

– Pool (ID): a Pool in normal status

– Pool (ID): the Pool usage rate exceeds the threshold value

– Pool (ID): a blocked Pool


Pool/volume list (i.e. the area in the upper right of the panel)

If you select Subsystem in the tree, the Pool/volume list displays the list of the Pools in the disk subsystem. When you selected Subsystem in the tree, the following items will be displayed in the Pool/volume list.

– Pool ID: Pool ID

– Capacity(GB): storage capacity of the Pool

– Used Capacity(GB): capacity of the Pool that is used by the Copy-on-Write Snapshot pairs

– Usage rate(%): usage rate of the Pool

– Pool Vol(s): total number of the Pool-VOLs in the Pool

– Snapshot pair(s): total number of snapshot data stored in the Pool

If you select a Pool icon in the tree, the Pool/volume list displays the list of the Copy-on-Write Snapshot pairs in the Pool.

– P-Vol: port ID, host group ID, the group number of host group or iSCSI target, and LUN of the P-VOL

– MU: snapshot ID

– Status: status of the Copy-on-Write Snapshot pair

– S-Vol: port ID, the group number of host group or iSCSI target, and LUN of the V-VOL

– Pool used(GB): capacity of the Pool that is used by the S-VOL

– Sync.: consistency rate of the data of the P-VOL and the S-VOL

Pool Association Inf.: X GB / Y GB

X indicates the capacity of the Pool association information in use.

Y indicates the total capacity of the Pool association information, including the capacity of the Pool association information in use.

Pool Mng. Block: X GB / Y GB

X indicates the capacity of the Pool management blocks in use.

Y indicates the total capacity of the Pool management blocks, including the capacity of the Pool management blocks in use.


Note: Pool association information and a Pool management block are the elements of V-VOL management area. You need to know the capacity of these two elements to calculate the number of Snapshot pairs you can create. For information about how to calculate the number of Snapshot pairs you can create, see section 2.2.

Pop-up menu (Pool/volume list)

When you selected a Pool icon in the tree, and then select and right click the Snapshot pairs in the Pool/volume list, a pop-up menu Pairsplit-S will be displayed. If you select this pop-up menu, the Pairsplit-S panel (Figure 3.12) will be displayed.

Preset list

Displays the content of the operations that have been set or specified in the C.O.W. Snapshot panel, but are still not applied to the USP subsystem. To apply the operations displayed in the Preset list to the subsystem, select the Apply button.

Preset list displays the following items.

– P-Vol: port ID, the group number of host group or iSCSI target, and LUN of the P-VOL

– MU: snapshot ID

– S-Vol: port ID, the group number of host group or iSCSI target, and LUN of the S-VOL

– Code: code that indicates the cause of the error*

– Preset X(Y): total number of the operations displayed in the Preset list(X) and the type of operation(Y)

Note*: If there is no error, --- will be displayed.

Pop-up menu (Pool/volume list)

When you select and right click the operations in the Preset list, the pop-up menu Delete will be displayed. If you select this pop-up menu, you can cancel the selected operation. The canceled operation will be deleted from the Preset list.

Apply button

Applies the operations displayed in the Preset list to the TagmaStore USP subsystem. If the specified operations complete successfully, the Preset list will be cleared. If an error occurs during an operation, the failed operation will remain in the Preset list. Details of the error (error code and message) are displayed on the error panel. For details about the list of the error code of Copy-on-Write Snapshot, please refer to the Storage Navigator™Error Codes.

Cancel button

Cancels all the operations set in the Preset list.


2.6.3.1 Preset List

The Preset list, in the lower right area in the ShadowImage Main panel, displays the content of the ShadowImage or Copy-on-Write Snapshot operations that have not been applied to the disk subsystem.

Figure 2.12 Preset List

The Preset list displays:

Port

The port ID (cluster and channel number) of the P-VOL is displayed.

G-ID

The group number of the host group or iSCSI target of the P-VOL is displayed.

LUN

The CU:LDEV (control unit image : logical device ID) of the P-VOL is displayed.

Note: An LDEV number that ends with a “#” mark indicates that the LDEV is an external volume (e.g. 00:01#). For details regarding the external volumes, please refer to the Universal Volume Manager User’s Guide.

MU

The snapshot ID of the Copy-on-Write Snapshot pair will be displayed. If the pair is in SMPL status, --- will be displayed. For details about what will be displayed in this item if you select ShadowImage pairs, please refer to the ShadowImage User’s Guide.

Port

The port ID (cluster and channel number) of the S-VOL is displayed. If there is no S-VOL, --- is displayed.

G-ID

The group number of the host group or iSCSI target of the S-VOL is displayed. If there is no S-VOL, dashes (---) are displayed.


LUN(S)

The CU:LDEV (control unit image:logical device ID) of the S-VOL is displayed. If there is no S-VOL, --- is displayed.

Note: An LDEV number that ends with a “V” mark indicates that the LDEV is an virtual volume (e.g. 00:01 V).

Pace


Capacity(MB)

The storage capacity of the volume is displayed. The unit is megabyte (MB).

CLPR(P)

The cache logical partition of the P-VOL is displayed.

CLPR(S)

The cache logical partition of the S-VOL is displayed.

Code

Code that indicates the cause of the error is displayed. If there is no error, --- will be displayed.

Pop-up menu

This menu appears when you select an item in the Preset list and right click it.

Table 2.18 Pop-up Menu of the Preset List in the ShadowImage Main Panel

Command Function

Delete Cancels the selected operation(s) in the Preset list.

Note: The grayed out commands are for ShadowImage pairs. For details about those commands, please refer to the ShadowImage User’s Guide.

Preset X(Y)

X indicates the total number of the operations displayed in the Preset list.

Y indicates the type of operation.

You can display only the specified volumes in the volume list if you specify the conditions in the Display Filter panel.


2.6.3.2 Display Filter

Figure 2.13 Display Filter panel showing the Copy-on-Write Snapshot Tab


CLPR dropdown list

Allows you to display the volumes in the specified cache logical partition (CLPR). If you select All from the dropdown list, the volumes in all the CLPRs will be displayed in the volume list.

Volume Type box

The following check boxes are displayed. Both check boxes are selected by default.

– Internal Vol: Displays or hides the internal volumes.

– External Vol: Displays or hides the external volumes.

Attribute box

The following check boxes are displayed.

– Reserved: This check box is for ShadowImage pairs. For details, please refer to the ShadowImage User’s Guide.

– Pair: Displays or hide the volumes that form pair(s).

– Non-Pair: Displays or hide the volumes in SMPL status.

– Cascade (L1 / L2 radio buttons): This check box is for ShadowImage pairs. For details, please refer to the ShadowImage User’s Guide.

Pair Status box

The following check boxes are displayed.

– ShadowImage: Displays or hides the ShadowImage pairs.

– C.O.W. Snapshot: Displays or hides the Copy-on-Write Snapshot pairs.

Note: If the check box is not selected, all the check boxes in each tab will be grayed out.

ShadowImage tab

This tab is for ShadowImage pairs. For details, please refer to the ShadowImage User’s Guide.

C.O.W. Snapshot tab

The check boxes that indicate the status of Copy-on-Write Snapshot pairs are displayed. If you select or deselect the check boxes, the Copy-on-Write Snapshot pairs in those statuses will be displayed or hidden in the volume list. To use the check boxes in the C.O.W. Snapshot tab, you must select the C.O.W. Snapshot check box in the Pair Status box.

For details about the status of a Copy-on-Write Snapshot pair, see section 3.1.

OK button

Applies the settings, and closes the Display Filter panel.

Cancel button

Resets the settings, and closes the Display Filter panel.


2.6.3.3 Pairsplit-S Panel

Figure 2.14 Pairsplit-S panel

The Pairsplit-S panel displays the following items.

Volume list

Information about the Copy-on-Write Snapshot pairs you are going to delete is displayed.

– Port: port ID (cluster and channel number) of the P-VOL

– G-ID: the group number of the host group or iSCSI target of the P-VOL

– LUN: CU:LDEV (control unit image:logical device ID) of the P-VOL

– MU: snapshot ID


– Port: port ID (cluster and channel number) of the S-VOL

– G-ID: the group number of the host group or iSCSI target of the S-VOL

– LUN(S): CU:LDEV (control unit image:logical device ID) of the S-VOL

– Type: emulation type

– Capacity(MB): storage capacity of the Copy-on-Write Snapshot pair

– CLPR(P): cache logical partition of the P-VOL

– CLPR(S): cache logical partition of the S-VOL

OK button

Closes the Pairsplit-S panel and display the list of the Copy-on-Write Snapshot pairs in the Preset list.

Cancel button

Cancels the operation and closes the Pairsplit-S panel.


2.6.4 Detail Panel

You can display the Detail panel by first displaying the ShadowImage Main panel then right clicking on a Copy-on-Write Snapshot pair from the volume list. You can then select Detail from the menu and the Detail panel will appear.

Note: If you select Detail in the pop-up menu when you are selecting a ShadowImage pair, the displayed Detail panel will be different from that of displayed when you select a Copy-on-Write Snapshot pair. For details, please refer to the ShadowImage User’s Guide.

Figure 2.15 Detail Panel for a Copy-on-Write Snapshot Pair

The Detail panel displays the following items.

P-Vol

CU number and LDEV number of the P-VOL is displayed.

Type

Emulation type of the P-VOL is displayed.

Capacity(MB)

Capacity of the P-VOL is displayed. The unit is megabyte (MB).

Blocks

The number of blocks used by the P-VOL is displayed.

CLPR(P)

The cache logical partition (CLPR) of the P-VOL is displayed.

Pool ID

Pool ID of the Pool in which the P-VOL is registered is displayed.

Amount of Pool use by P-Vol(GB)

Amount of the Pool capacity that is used by the P-VOL is displayed.


Pool usage rate by P-Vol

Pool usage rate of the P-VOL is displayed.

Snapshot Pair Detail list

Following information items of snapshot data is displayed.

– MU: snapshot ID

– S-Vol: CU number and LDEV number of the S-VOL


– Time: time at when the snapshot data is stored in the Pool

– Pool used(GB): capacity of the Pool that is used by the S-VOL

– Sync.: consistency rate of the data of the P-VOL and the S-VOL

– CLPR(S): cache logical partition (CLPR) of the S-VOL

Refresh button

Updates the information in the Detail panel.

OK button

Closes the Detail panel.


Chapter 3 Using Copy-on-Write Snapshot

3.1 Copy-on-Write Snapshot Overview

Copy-on-Write Snapshot creates a volume pair from a primary volume (P-VOL), which contains the original data, and a virtual volume (V-VOL), which contains the snapshot data. Copy-on-Write Snapshot uses the V-VOL as the secondary volume (S-VOL) of the volume pair. Since each P-VOL is paired with its V-VOL independently, each volume can be maintained as an independent copy set.

Snapshot operations can be performed from a UNIX® and/or PC server host using the CCI software. Copy-on-Write Snapshot commands are issued from the Command Control Interface (CCI) through the command device in the storage system.

3.1.1 Copy-on-Write Snapshot work flow

You need to use Storage Navigator to create the Pools and V-VOLs. You can also use Storage Navigator to delete pairs. Use the CCI to create Copy-on-Write Snapshot pairs and perform subsequent operations.

66 Chapter 3 Using Copy-on-Write Snapshot

Creating pool

Creating Copy-on-Write Snapshot pair

Deleting Copy-on-Write Snapshot pair

Storing snapshot data in the pool

Creating virtual volume

Restoring Copy-on-Write Snapshot pair

In case of failure

Deleting snapshot data

Initializing V-VOL management area

Figure 3.1 Procedure for Using Copy-on-Write Snapshot

Notes:

– The virtual volume management area must be created in shared memory before creating a Pool. The virtual volume management area is automatically created when additional shared memory is installed. For details on installing additional shared memory, please call the Support Center.

– Please initialize the V-VOL management before you start using Copy-on-Write Snapshot for production purposes, for details, see section 3.1.3. Delete any Pools or Copy-on-Write Snapshot pairs that were created for testing purposes.


Caution: Using a non-host application to monitor Copy-on-Write Snapshot pair volumes may cause instability in the monitoring application and port access, and in some cases, it may cause the application to unexpectedly terminate. For example, if the V-VOL whose status is not PSUS (or PFUS), rejects the access from the host, instability may occur in the monitoring application software when its access is rejected. In addition, if the host computer connects to more than one port, trouble may also occur on the ports that are not connected to the V-VOL that rejected the host access. You must quit the monitoring application to solve these problems. For details about the relations between the pair status and host access, see Table 3.2.

You do not always need to delete the Copy-on-Write Snapshot pairs after storing snapshot data in the Pool. Since one P-VOL can be paired with up to 64 S-VOLs, you need to delete the snapshot data or the unnecessary pairs to delete the links. When you delete a Copy-on-Write Snapshot pair, the pair’s snapshot data will also be deleted from the Pool. For additional information about deleting snapshot data and Snapshot pairs, please refer to section 3.7

If a failure occurs when you restore a Copy-on-Write Snapshot pair, its snapshot data is written back to the P-VOL. You may not be able to restore the pair if another pair is being restored.

For details about the status of the Copy-on-Write Snapshot pair and the operations on the pair, see section 3.9.


3.1.2 Displaying the ShadowImage Main panel

The ShadowImage Main panel is the primary interface to the Copy-on-Write Snapshot controls.

To display the ShadowImage Main panel:

1. Start Storage Navigator.

2. Select the ShadowImage start button.

The ShadowImage Main panel is displayed.

Figure 3.2 ShadowImage Main panel

Note: Though the ShadowImage Main panel displays information about both ShadowImage and Copy-on-Write Snapshot pairs, this section explains only the items displayed on the C.O.W. Snapshot tab. For details about the items related to the ShadowImage pairs, please refer to the ShadowImage User’s Guide.


3.1.3 Creating the Virtual Volume Management Area

To use Copy-on-Write Snapshot a V-VOL management area needs to be created in shared memory. The V-VOL management area is important for associating the V-VOL with the Pool-VOL. The V-VOL management area is created automatically when the additional shared memory is installed. Please call the Support Center for the installation of additional shared memory.

There are two kinds of areas in the V-VOL management area; Pool management block and Pool association information. When you create Pools or Snapshot pairs, the Pool management block or Pool association information will be stored in the V-VOL management area which reduces its available capacity. When the capacity of the V-VOL management area is exhausted, the capacity ratio of the Pool management block and the Pool association information in the V-VOL management area will be fixed. Problems may occur if the Pool management block has insufficient capacity and you may not be able to create new Pools or create Pools with a large capacity. To solve such problems, you need to initialize the V-VOL management area.

3.1.3.1 Initializing the V-VOL Management Area

Initializing the V-VOL management area provides greater storage efficiency allowing you to create a Pool whose capacity is larger than would have been possible if the V-VOL Management Area had not been initialized, and you will be able to create more Pools than before the initialization.

You need to delete all Pools in the disk subsystem in order to initialize the V-VOL management area. If Pools exist in the disk subsystem, only the Pool management block will be initialized instead of the whole V-VOL management area. For details about initializing the Pool management block, see section 3.1.3.2.

To initialize the V-VOL management area:

1. Switch to the Modify mode in Storage Navigator.

For the information about how to change the mode, please refer to the Storage Navigator™ User’s Guide.

2. Select the Initialize button in the Pool panel.

A confirmation message is displayed to ask you if it is OK to initialize the V-VOL management area or the Pool management block.

3. Select OK.

The confirmation message asks you if it is OK to cancel all the operations performed in the Pool panel.

4. Select OK.

The confirmation message asks you if it is OK to apply the setting to the disk subsystem and perform the initialization.

5. Select OK.

The V-VOL management area is initialized.


3.1.3.2 Initializing the Pool Management Block

If you initialize the Pool management block, I/O performance of the Pool will improve compared to before initialization. You can initialize the Pool management block without changing the Pools already created in the disk subsystem.

Note: The Pool management block may need up to 20 minutes to initialize.

To initialize the Pool management area:

1. Switch to the Modify mode in Storage Navigator.

For the information about how to change the mode, please refer to the Storage Navigator User’s Guide.

2. Select the Initialize button in the Pool panel.

The confirmation message is displayed to ask you if it is OK to initialize the Pool management block.

3. Select OK

The confirmation message is displayed to ask you if it is OK to cancel all the operations performed in the Pool panel.

4. Select OK

The confirmation message is displayed to ask you if it is OK to apply the setting to the disk subsystem and perform the initialization.

5. Select OK

The Pool management block is initialized.


3.2 Creating and Deleting Pools

While reading this section, pay special attention to information concerning Pool capacity and the volume types that will be specified as Pool-VOLs. This section provides Pool capacity definitions and information about using external volumes as Pool-VOLs.

3.2.1 Creating the Pool

The Pool stores the snapshot data captured by Copy-on-Write Snapshot. An ordinary Pool consists of multiple Pool-VOLs. Up to 1024 Pool-VOLs can be registered in a Pool, and 128 Pools can be created in a disk subsystem.

Figure 3.3 illustrates the relationship between Copy-on-Write Snapshot pair and a Pool.

Example : flow of data

Copy-on-Write Snapshot pair

V-VOL

A

C

BB

C

A

P-VOL

Pool (pool-VOLs)

D

Figure 3.3 The Mechanism of Copy-on-Write Snapshot Pair and Pool

3.2.1.1 Defining Pool capacity

You must create a Pool to use Copy-on-Write Snapshot. To create a Pool, use the Pool panel of the Storage Navigator, see section 2.5.2.


The Pool capacity is the total capacity of the Pool-VOLs defined in the Pool. When you create a Pool, you must estimate the copy capacity (e.g. the capacity of the snapshot data to be copied to the Pool) and set enough Pool capacity for the estimated copy capacity, see section 2.2. Set enough Pool capacity for the largest copy capacity as the copy capacity requirements may fluctuate over time. The status of the Copy-on-Write Snapshot pairs can change to PSUE if you exceed the defined capacity of the Pool.

WARNING: The capacity of a Pool is equal to the total capacity of registered Pool-VOLs in the Pool. If the usage rate of the Pool exceeds its capacity, the status of the Copy-on-Write Snapshot pair changes to PSUE (status when failure occurred). If this happens, snapshot data cannot be stored in the Pool and the Copy-on-Write Snapshot pair must be deleted. Please refer to Table 4.1 and section 3.7.

Note:

– When snapshot data is copied to a Pool, a multiple of 256 KB of the Pool will be consumed. Even if the capacity of the snapshot data is less than 256 KB, you need 256 KB area in the Pool for the data.

– If the same area in the P-VOL is updated more than one time, the snapshot data for the area is copied to the Pool only when the first update was taken place. Therefore, when the same area in the P-VOL is updated only once, the written data capacity is equal to the copied data capacity. However, when the same area in the P-VOL is updated repeatedly, the copy capacity will be smaller than the written data capacity.

– Use a volume whose capacity is a multiple of 256 KB as a Pool-VOL, any capacity less than 256 KB will be rounded off. For example, if you add a volume of 100.125 MB as a Pool-VOL, 125 KB will be rounded off and the capacity of the Pool will increase only by 100 MB.

Pool-VOLs registered in a Pool can be added but cannot be deleted during operation. In addition, the entire snapshot data in the Pool needs to be deleted in order to delete the Pool itself.

When estimating copy capacity, you need to consider whether there is only one snapshot or several.

One snapshot

If the same area in the P-VOL is updated only once, the copy capacity is equal to the capacity of the data that is written between the storing and the deletion of the snapshot data.

For example, if you want make a backup by using Copy-on-Write Snapshot, you can backup the data from the V-VOL after storing the snapshot data, and then delete the snapshot data. In this case, only the data that was written during the backup need to be copied to the Pool, and there is only one snapshot data. Therefore, you can make a backup with the Pool of small capacity. However, since you need to read a large amount of data from the S-VOL during the backup, the access to the P-VOL increases and consequentially the host I/O performance may be lowered.

Multiple snapshot data


After the storing of each snapshot data, if the same area in the P-VOL is updated only once until the snapshot data is deleted, the copy capacity is equal to the capacity of the data that is written between the storing and the deletion of the snapshot data. If there is more than one P-VOL, the copy capacity is equal to the total capacity of the data written to each P-VOL.

Note: When you store more than one snapshot in the Pool, some snapshot pairs may share data in the Pool. While the snapshot data are shared, you can delete the pairs but you cannot delete the shared snapshot data from the Pool. The shared snapshot data will not be deleted from the Pool until all the Copy-on-Write Snapshot pairs that share the data are deleted.

3.2.2 Using External Volumes as Pool-VOLs If the Universal Volume Manager is installed, you may connect multiple disk subsystems to the TagmaStore subsystem. In that case, the original TagmaStore subsystem is the local subsystem, and the connected storage subsystems are the external subsystems. A volume in an external subsystem is the external volume. A volume in the local subsystem is the internal volume. Both internal and external volumes can be used as Pool-VOLs

Caution: External volumes are more likely to fail than internal volumes. In addition, resolving external volume failures is more complex than resolving internal volume failures. If you use both internal and external volumes as Pool-VOLs for one Pool, or if you specify external volumes from several external subsystems for one Pool you risk triggering faults that may result in a volume blockade. For example, if a fault occurs and the external Pool-VOL is blocked, the entire Pool becomes blocked as well. For information about recovering a blocked Pool, see section 4.2.1.

In order to minimize the risk of volume failure, please use external volumes as follows:

– Specify external volumes from only one external subsystem to create a Pool

– Do not combine both internal and external volumes into one Pool

For details about external subsystems and solutions for resolving errors related to external volumes, refer to the Universal Volume Manager User’s Guide.

3.2.3 Creating New Pools

The time required to create Pools depends upon the number and the capacity of the Pools and Pool-VOLs that you want to add to the Pool. If you are going to create many Pools, or if you add a Pool-VOL with a large capacity, you may wait about 20 minutes or so until volume processing is complete.




3. Select the Pool tab.

The Pool panel is displayed. Using this panel you can create or delete Pools.


Figure 3.4 Pool Panel

You can also initialize the V-VOL management area or the Pool management block by using the Pool panel. For details, see section 3.1.3.

Note: You need to keep the capacity of the Pool management blocks in use less than its total capacity.


4. Change the mode of the Storage Navigator to Modify.

For information how to change the mode, please refer to the Storage Navigator™ User’s Guide.

5. Right click C.O.W. Snapshot in the Pool tree of the Pool panel (Figure 3.4).


6. Select New Pool from the pop-up menu.

Figure 3.5 New Pool Panel

7. Enter the Pool ID in the Pool ID text box.

Note: You can enter only a whole number from 0 to 127 in this text box. Do not enter any number that is already used for another Pool.

8. Select the threshold of the Pool usage rate from the Threshold dropdown list.

Caution: If the usage rate of the Pool exceeds the threshold, you cannot create new Copy-on-Write Snapshot pairs. Make sure you do not set too small a value for the threshold. Please see Table 4.1 for threshold troubleshooting options.

9. Select C.O.W. Snapshot from the Attribute dropdown list.

10. Check the contents of the setting and if there is no problem, select the Set button.

The New Pool panel closes and the new Pool will be displayed in the Pool tree.

11. Select the Pool in the Pool tree.

12. Select the volumes which you want to register in the Pool as the Pool-VOLs from the Free LDEVs list.

Note:

– If you select the CU number from the CU dropdown list, the volumes in the CU will be displayed in the list. Within the same CU, you can select the multiple volumes at a time.

– The capacity of the Pool management blocks in use will increase if you add the Pool-VOLs. You need to be careful to keep the capacity of the Pool management blocks in use less than its total capacity.


13. Select the Add Pool-VOL button.

The panel that lists the volumes you selected in step 12 is displayed.

Note: If you select and right click the volume in the Free LDEVs list, a pop-up menu will be displayed. If you select Add Pool-VOL from the pop-up menu, the result will be the same as when you selected the Add Pool-VOL button.

14. Check the list of the volumes on the panel and if there is no problem, select the OK button.

The panel closes and the selected volumes will be displayed in the Pool-VOL list.

15. If you want to add more Pool-VOLs, repeat steps 12 through 14.

Note: Total capacity of the Pool-VOLs in the Pool is the storage capacity of the Pool. See section 3.2.1 for notes on creating a Pool.

16. If you want to create another Pool, repeat steps 5 thru 14

17. Select the Apply button.

The confirmation message is displayed to ask you if it is OK to apply the setting to the disk subsystem.

Caution: You cannot delete the Pool-VOLs once you’ve added them. Make sure to verify the settings for the Pool-VOLs before selecting Apply.

18. Select the OK button.

The confirmation message closes and the new Pool information is applied to the subsystem.


3.2.4 Changing Pool Information

After you’ve created the Pool, you can only change the threshold setting.

To change the threshold of the Pool:


If the mode is already changed to Modify, you can skip this step. For the information how to change the mode, please refer to the Storage Navigator™ User’s Guide.

2. Select and right click the Pool whose setting you want to change.


Note: If the Pool usage rate is 95 % or higher, the pop-up menu will not be displayed.

3. Select Change Pool Information from the pop-up menu.

The Change Pool Information panel is displayed.

Figure 3.6 Change Pool Information Panel

4. Select the value for the threshold from the Threshold dropdown list.

Note: In the dropdown list, only the values that are higher than the Pool usage rate are displayed.

5. Select the Set button.

The Change Pool Information panel closes.




The confirmation message closes and the change of the setting is applied to the subsystem.

The items in the Change Pool Information panel are same with those of the New Pool panel. However, in the Change Pool Information panel, you cannot enter or select the items other than the Threshold dropdown list. For details about the items in the Change Pool Information panel, see section 3.2.3.


3.2.5 Deleting Pools

You can either delete individual Pools, or a group of Pools at a time. You have greater control over Pool deletions when you delete them individually. Deleting Pools by group offers greater efficiency, but all Pools in the group are deleted. If there are any Pools in the group to be deleted that you wish to retain, you must delete the Pools in that group individually.

3.2.5.1 Deleting Individual Pools

To delete a single Pool:

1. If the Storage Navigator is not in the Modify mode, select that mode now.

2. Right click the Pool you want to delete and select Delete Pool from the pop-up menu.

3. Select the OK button in the confirmation message.

The icon of the selected Pool changes to the icon which indicates the deleting process.

4. Select the Apply button and select OK in the confirmation message to apply the setting to the disk subsystem.

The confirmation message closes and Pool deletion in the subsystem begins.

3.2.5.2 Deleting Multiple Pools

Caution: If you execute these steps, all Pools selected for deletion will be deleted. If there is any Pool in the group that you do not want to delete, you will have to delete one Pool at a time. See section 3.2.5.


2. Right click the C.O.W. Snapshot icon in the Pool tree of the Pool panel.

3. Select Delete Pool(s) from the pop-up menu and select OK in the pop-up confirmation message to delete the Pools.

The icons of the Pools change to show the Pools that are being deleted.

4. Select the Apply button and select OK in the confirmation dialog box.

The confirmation message closes and Pool deletion in the subsystem begins.


3.3 Creating and Deleting Virtual Volumes

3.3.1 Creating New Virtual Volumes

The V-VOL is defined in a VDEV and needs to be created before you create a Copy-on-Write Snapshot pair. The V-VOL definition cannot be released if it is currently being used in a Copy-on-Write Snapshot pair. To release the definition, you must delete the Copy-on-Write Snapshot pair that uses the V-VOL. To delete a Copy-on-Write Snapshot pair, see section 3.7.

Caution: If you are using HP-UX as a host server, mind the followings when you execute the command on V-VOLs in order to recognize the device from the host server.

– If the device is already recognized by the host server, do not change its volumes to V-VOLs.

– Before executing the command to recognize the device, create Copy-on-Write Snapshot pairs and store snapshot data.

If you do not follow the cautions above, an error may occur and the host server may be terminated. When the host server is terminated because of the command to recognize the device, retry the command by following the steps below.

1. Force the command process and its parent process to terminate.

2. Create a Copy-on-Write Snapshot pair.

3. Store the snapshot data in the Pool.

4. Execute the command again to recognize the device.

Note:

– Servers including CCI, will show 0 (zero) and you will see OPEN-0V on the screen when the emulation type of a V-VOL is in OPEN-V. When you create a Copy-on-Write Snapshot pair, specify the volume whose emulation type is displayed as OPEN-0V for the V-VOL.

– You must define a V-VOL group before creating a V-VOL. OPEN-V is the emulation type for VDEV, including a V-VOL group, and a V-VOL. Because the capacity of the VDEV is 2 TB, the maximum capacity of a V-VOL is 2 TB.


To create new virtual volumes:


For the information how to change modes, please refer to the Storage Navigator™ User’s Guide.

2. Right click Subsystem in the V-VOL group tree of the V-VOL panel.


3. Select New V-VOL Group from the pop-up menu.

The New V-VOL Group panel (Figure 3.7) is displayed.

Figure 3.7 New V-VOL Group Panel

4. Enter the V-VOL group ID in the V-VOL Group dropdown list.

Note: You can either select or enter any whole number from 1 to 8192 in the dropdown list. Do not enter any number already used for another V-VOL group.

5. Select the emulation type of the V-VOL group from the Emulation Type dropdown list.

6. Select the CLPR number of the CLPR in which you want to register the V-VOL group from the CLPR dropdown list.


7. Select the Next button.

The Create V-VOL wizard panel (1) is displayed.


8. Select the emulation type of the V-VOL from the Emulation Type dropdown list.

9. Select the unit of the capacity of the V-VOL from the Capacity Unit dropdown list.

The selected unit is displayed after the Capacity text box.

10. Enter the capacity of the V-VOL in the Capacity text box.

Note:

– If you’re using megabytes (MB), you can enter only whole numbers between 46 and 2097151. If you’re using blocks, enter whole numbers between 96000 and 4294967296. If you’re using cylinders, enter whole numbers between 50 to 2236962.

– The V-VOLs you are creating will be used when you specify them as S-VOLs of the Copy-on-Write Snapshot pairs. Since the capacity of the P-VOL and the S-VOL (V-VOL) of the Copy-on-Write Snapshot pair must be equal, consider the capacity of the P-VOLs when you decide the V-VOL capacity.

11. Enter the number of the V-VOLs you want to create in the Number of V-VOL text box.

Note: You can enter only whole numbers between 1 and 256 in this text box.


12. Select the Set button.

The volumes are added to the V-VOL information setting list (i.e. middle of the panel). If you want to create additional V-VOLs, repeat step 8 to step 12.

Note: Once the V-VOL group is created, additional V-VOLS cannot be added it without deleting the pairs and starting again. Make sure to add enough V-VOLs to create the Copy-on-Write Snapshot pairs now.




14. Select the volume in the V-VOL information setting list (i.e. upper right area of the panel).

15. Select the CU number from the Select CU No. dropdown list.

Areas of the CU selected from the dropdown list are displayed in the Select LDEV No. area (i.e. middle of the panel).

Note:

– Only the areas displayed by the white cells are available for the V-VOLs. You cannot use the areas displayed by the gray cells to create the V-VOLs.

– If you want to select the CUs that belongs to other SLPRs, select the CU number of another SLPR is used. check box.


16. Select the interval between the LDEV numbers from the Interval dropdown list. Note: If you select 0, the LDEV number will be sequential.

17. Select the area in the Select LDEV No. area.

The color of the selected area changes to blue. CU number and LDEV number are added to the V-VOL information setting list, and the blue italic fonts changes to the black normal fonts.

If there are multiple V-VOLs to set, repeat the step 14 to step 17.




19. Check the settings and if there is no problem, select the OK button.

The Create V-VOL wizard panel (3) closes and the V-VOL panel is displayed again.

In the V-VOL panel, the settings are displayed in the blue italic fonts.




The confirmation message closes and the new V-VOL information is applied to the subsystem.


3.4 Using LUSE to create a Virtual Volume

To display the V-VOL panel:




3. Select the V-VOL tab.

Figure 3.11 V-VOL Panel

Note: In the V-VOL panel, you create or delete the V-VOLs per a V-VOL group. If you want to create or delete a V-VOL by itself, use the Virtual LVI/LUN function. For details about the Virtual LVI/LUN function, please refer to the LUN Expansion/ Virtual LVI/LUN User’s Guide.


3.4.1 Deleting Virtual Volumes

To delete V-VOL(s):



2. In the V-VOL group tree in the V-VOL panel, select and right click the V-VOL group which contains the V-VOL(s) you want to delete.


3. Select Delete V-VOL Group from the pop-up menu.

The confirmation message is displayed to ask you if it is OK to delete the selected V-VOL group.


The icon of the selected V-VOL group changes to the icon which indicates the deleting process.




The confirmation message closes and the deletion of the V-VOL group is applied to the subsystem.

Note: You cannot delete the V-VOL if it is used as the secondary volume of the Copy-on-Write Snapshot pair. If you want to delete a V-VOL that is used as a secondary volume, first delete the Snapshot pair.


3.5 Creating Copy-on-Write Snapshot Pairs

A Copy-on-Write Snapshot pair uses a V-VOL as its secondary volume. Therefore, you need to create a V-VOL before creating a Copy-on-Write Snapshot pair. See section 3.3 for more information about creating V-VOLs.

Caution: When creating a Copy-on-Write Snapshot pair, you must decide which Pool will be used by the pair. If you create two or more Copy-on-Write Snapshot pairs that share the same P-VOL, you need to specify the same Pool for these pairs. For example, if you specify three V-VOLs for one P-VOL, you need to specify the same Pool for these three pairs.

Note: You cannot create Snapshot pairs using SMPL(PD) volumes. If the volumes are in the SMPL(PD) status, wait and issue the paircreate command after the volume status changes to SMPL.

When you delete a Copy-on-Write Snapshot pair, the status of the volumes becomes SMPL(PD). This status continues for several seconds, and sometimes more than ten minutes. The time the volume stays in SMPL(PD) status increases if the deleted pair used a large amount of the Pool. When the deletion process is complete the status changes to SMPL. Use the ShadowImage main panel to see the status of the volume. Using the CCI, you can check the volume status using the pairdisplay command, but you will not be able to distinguish between an SMPL volume and an SMPL(PD) volume. To distinguish between these volumes, you need to issue inqraid as well. The inqraid command will show you if the volume is being used by Copy-on-Write Snapshot. If the volume is not being used, its status will be SMPL. If the volume is used, its status will be SMPL(PD).

Up to 64 V-VOL secondary volumes can be specified per P-VOL in a Copy-on-Write Snapshot pair.

Use the paircreate command in the CCI to create Copy-on-Write Snapshot pairs. The conditions below must be met when creating Snapshot pairs.

– Specify a P-VOL volume that meets the requirements listed in Table 2.3.

– Specify a V-VOL volume that meets the requirements listed in Table 2.4.

– Specify the P-VOL and V-VOL volume sizes. The P-VOL and V-VOL volume sizes must be identical.

– When you use a volume that is already used as the P-VOL of another pair for the P-VOL of the new pair, specify the same Pool for the pairs which share the P-VOL.


When using CCI commands to control Snapshot pairs, whether or not operations complete normally depends on the status of the pairs. The table below shows the pair status and the results of the CCI commands.

Table 3.1 Pair Statuses and the Results of the CCI Commands

CCI Command No. Pair Status

paircreate paircreate –split

pairsplit pairresync pairresync -restore

pairsplit -S

pairsplit -E

1 SMPL OK No No No No NOP No

2 COPY NOP No No NOP NOP No No

3 PAIR / PFUL NOP OK OK NOP NOP OK No

4 PSUS / PFUS No NOP NOP OK OK OK No

5 SMPL(PD) No No No No No NOP No

6 COPY(RS) NOP No No NOP NOP No No

7 COPY(RS-R) NOP No No NOP NOP No No

8 PSUE No No No OK* No OK NOP

OK: The command executes the process and ends normally.

NOP: The command does not execute the process but ends normally.

No: The command ends abnormally (i.e., command rejected).

Note*: If you issue pairresync to the pair whose status has changed to PSUE because of the shortage of the shared memory for the V-VOL management area, the command will be rejected and end abnormally.

When the command executes the process and ends normally, the pair status changes according to the process. For information about how the pair status changes when the command ends normally, see Figure 3.14 and paragraphs below that figure.

For additional information about the CCI commands used in this section, please refer to the Command Control Interface (CCI) User and Reference Guide.


3.6 Storing Snapshot Data

Snapshot data is a replica of the data in the P-VOL of a Copy-on-Write Snapshot pair, and is stored in a Pool. When the P-VOL is updated, the updated part of the data is copied to the Pool as snapshot data before the P-VOL is updated. This process is called storing snapshot data.

If you issue a command to a Copy-on-Write Snapshot pair to store snapshot data, the data will be stored in the Pool at a later time when a host makes a write request to the P-VOL of a Snapshot pair. A Snapshot pair can store up to 64 snapshot data objects per P-VOL.

To store snapshot data in a Pool, use the pairsplit command in the CCI. You can store a maximum of 64 snapshot data objects per P-VOL. To store snapshot data, the pair status must be set to PAIR. For details about the steps necessary to store snapshot data, see section 3.6.

Note: When a P-VOL is paired with two or more volumes, make sure that the pairs are not in COPY(RS-R) status.

You can store one snapshot data object at a time by using pairsplit, but you cannot specify the snapshot data ID. For details about using the pairsplit command, please refer to the Command Control Interface (CCI) User and Reference Guide.

Note: Copy-on-Write Snapshot does not support Quick Split mode. If you specify Quick Split mode, snapshot data will not be stored in the Pool even if the command ends normally.


3.7 Deleting Snapshot Data and Snapshot Pairs

The Pool capacity is the total capacity of the Pool volumes defined in the Pool. The status of the Copy-on-Write Snapshot pairs can change to PSUE if you exceed the pre-defined capacity of the Pool as a result of writing data in the volume of that pair. When the status changes to PSUE, additional snapshot data cannot be stored in the Pool, and new pairs cannot be created until unnecessary snapshot data is deleted. You can store up to 64 snapshot data objects per P-VOL.

There are 2 ways to delete snapshot data. One way is to delete the Copy-on-Write Snapshot pair itself, and the other way is to delete only the snapshot data.

When a Snapshot pair is deleted, snapshot data stored in the Pool is deleted and the relationship between P-VOL and V-VOL is released. However, if only the snapshot data is deleted, the relationship between P-VOL and V-VOL is maintained and the snapshot ID of the deleted snapshot data can be assigned to the newly stored snapshot data of the Copy-on-Write Snapshot pair.

Use pairresync in the CCI to delete snapshot data. However, if the snapshot data you are trying to delete shares a data area with another snapshot data object, only the snapshot ID will be deleted, the data itself will not be deleted from the Pool. You can also use the pairsplit –S in the CCI, or the Pairsplit-S panel of the Storage Navigator, to delete Snapshot pairs. You can delete only one pair at a time when using pairsplit –S. You can delete multiple pairs at a time if you use the Pairsplit-S panel.

You can open the Pairsplit-S panel either from the ShadowImage Main panel or the C.O.W. Snapshot panel. If you want to select the pairs to be deleted by port, host group, iSCSI target, or LUN, open the Pairsplit-S panel from the ShadowImage Main panel. If you want to select the pairs by Pool, open the Pairsplit-S panel from the C.O.W. Snapshot panel.

Notes:

– After the command is issued to delete snapshot data, no additional snapshot data from that Copy-on-Write Snapshot pair will be stored in the Pool even if the host tries to write data in the P-VOL. If you want to store snapshot data of that Copy-on-Write Snapshot pair again, you need to issue the command for storing snapshot data.

– The required time for deleting snapshot data or Copy-on-Write Snapshot pairs is several seconds, and sometimes more than ten minutes. The time will increase if the deleted pair uses large amount of the Pool, or if multiple pairs are deleted at one time.

– When you delete a Copy-on-Write Snapshot pair, the status of the volumes becomes SMPL(PD). Use the ShadowImage Main panel to see the status of the volume. Using the CCI, you can check the volume status using the pairdisplay command, but you cannot distinguish between an SMPL volume and an SMPL(PD) volume. To distinguish between these volumes using CCI, you need to issue inqraid as well. The inqraid command will show you if the volume is being used by Copy-on-Write Snapshot. If the volume is not used, its status is SMPL. If the volume is used its status is SMPL(PD).


– Copy-on-Write Snapshot does not support Quick Resync mode. If you specify Quick Resync, snapshot data will not be deleted even if the command ends normally.

– As the number of disk adaptors used in the disk subsystem increases, the amount of time required to delete snapshot data or Snapshot pairs decreases. Because the TagmaStore NSC has fewer disk adaptors than the TagmaStore USP, the NSC requires more time to delete snapshot data or Snapshot pairs even when running the same operations.

3.7.1 Deleting Copy-on-Write Snapshot Pairs by Selecting the Pairs per Port

To delete Copy-on-Write Snapshot pairs by selecting the pairs per port:


2. Select the ShadowImage Main panel.

3. In the tree, select the port, host group, iSCSI target, or LUN that contains the Copy-on-Write Snapshot pairs you want to delete.

The list of the pairs or volumes is displayed in the volume list.

4. Select and right click the Copy-on-Write Snapshot pairs you want to delete.


Note: You cannot delete a ShadowImage pair and a Copy-on-Write Snapshot pair at the same time.

5. Select Pairsplit-S from the pop-up menu.

The Pairsplit-S panel is displayed.

Figure 3.12 Pairsplit-S panel



The Pairsplit-S panel closes and the list of the Copy-on-Write Snapshot pairs that you are going to delete will be displayed in the Preset list of the ShadowImage Main panel.




The confirmation message closes and the deletion of the pair is applied to the subsystem.

Note: For details about the Pairsplit-S panel that will be displayed when you selected ShadowImage pairs, please refer to the ShadowImage User’s Guide.

3.7.2 Deleting Copy-on-Write Snapshot Pairs by Selecting the Pairs per Pool

To delete Copy-on-Write Snapshot pairs by selecting the pairs per Pool:

1. Start the Storage Navigator and display the Storage Navigator main panel.





4. Select the C.O.W. Snapshot tab.

C.O.W. Snapshot panel (Figure 3.13) is displayed.

5. In the tree, select the Pool that contains the Copy-on-Write Snapshot pairs you want to delete.

The list of the pairs or volumes is displayed in the volume list.

6. Select and right click the Copy-on-Write Snapshot pairs you want to delete.


7. Select Pairsplit-S from the pop-up menu.

The Pairsplit-S panel (Figure 3.12) is displayed.


The Pairsplit-S panel closes and the list of the Copy-on-Write Snapshot pairs that you are going to delete will be displayed in the Preset list of the C.O.W. Snapshot panel.





The confirmation message closes and the deletion of the pair is applied to the subsystem.

Figure 3.13 C.O.W. Snapshot Panel


3.8 Restoring a Copy-on-Write Snapshot Pair

Use pairresync -restore of the Command Control Interface to restore Copy-on-Write Snapshot pairs. The Snapshot pair must be in PSUS status when you restore the pair.

When the restoration completes, the pair status changes to PAIR. For details about pairresync -restore, please refer to the Command Control Interface (CCI) User and Reference Guide.

WARNING: If a failure occurs during the restoration, the pair status changes to PSUE. To recover the PSUE pair, you need to delete the snapshot data of the pair. When you recover the PSUE pair by deleting its snapshot data, data in the P-VOL will not be guaranteed. Therefore, you need to overwrite the P-VOL with the backup data or format the P-VOL.

Copy-on-Write Snapshot can restore the contents of the P-VOL to the state when the snapshot data was stored in the Pool by writing the snapshot data back to the P-VOL. Writing the snapshot data back to the P-VOL is called restoration of Copy-on-Write Snapshot pair.

Note: If you restore the pair when the data is written in the S-VOL, instead of the snapshot data, the data in the S-VOL will be written back to the P-VOL.

If there are problems with the data of P-VOL during a failure, you can restore the P-VOL to the normal state when the snapshot data was stored, by executing restoration.

Note: Copy-on-Write Snapshot does not support Quick Restore mode. If you specify Quick Restore mode, Copy-on-Write Snapshot pair will not be restored even if the command ends normally.


3.8.1 Copy Threshold Option

When set, the Copy Threshold option can minimize the degradation of host I/O performance by temporarily stopping copy processing caused by restore operations when the subsystem load is heavy.

When the load on the TagmaStore USP subsystem increases, host server I/O performance may become degraded. If Copy-on-Write Snapshot performs a restore operation while the subsystem load is heavy, it is more likely that host server I/O performance will become degraded. The Copy Threshold option temporarily stops copy processing caused by the restore operation when the subsystem load is heavy.

The Copy Threshold option is effective only when the subsystem load is heavy. When the Copy Threshold option is in effect, all the copy processing by the restore operation stops. For information about setting the Copy Threshold option, please call the Support Center.

Note: Copy operations that are stopped by the Copy Threshold option will resume when the subsystem load lightens. If this option is in effect, not only Copy-on-Write Snapshot copy operation but also the copy operations of the following program products will stop during heavy subsystem load.

– ShadowImage

– ShadowImage for z/OS

– Compatible Mirroring for IBM FlashCopy

– Compatible Mirroring for IBM FlashCopy Version 2

– Cross-System Copy

– Volume Migration


3.9 Copy-on-Write Snapshot Pair Status

When you create or split a Copy-on-Write Snapshot pair, the status of the pair changes. Figure 3.14 shows the transitions of the status of a Copy-on-Write Snapshot pair.

1. SMPL

2. Creating a pair (COPY)

S-VOLP-VOL

PAIR / PFUL

S-VOLP-VOL

PSUS / PFUS

5. Restoring a pair (COPY(RS-R))

（SMPL(PD)）

S-VOLP-VOL

PAIR

S-VOL P-VOL

6. PSUE

4. Deleting a pair

3. Storing Snapshot data in the pool

Failure

Pool usage exceeds the threshold

4. Deleting snapshot data(COPY(RS))

4. Deleting a pair

Figure 3.14 Copy-on-Write Snapshot Pair Status Transitions


1. If a volume is not assigned to a Copy-on-Write Snapshot pair, its status is SMPL.

2. Use paircreate on the SMPL volume to create a Snapshot pair. When you create the first pair for the P-VOL, the pair status changes to COPY, and then changes to PAIR when the operation completes.

If you specify a volume which is already paired with one or more V-VOLs as the P-VOL to create another pair, the pair status will not change to COPY, and the pair status will change to PAIR when the operation completes.

Note:

– It may take time to create a new pair if you use paircreate immediately after deleting the last snapshot data of the P-VOL.

– If the Pool capacity exceeds the threshold when a Copy-on-Write Snapshot pair is in PAIR status, the pair status changes to PFUL in Command Control Interface. For details, please refer to the Command Control Interface (CCI) User and Reference Guide.

– If you use paircreate when the Pool capacity exceeds the threshold, the command will be rejected and the pair will not be created.

3. Use pairsplit on the Snapshot pair in PAIR status to store the snapshot data in the Pool. When the operation completes, the pair status changes to PSUS.

Note: If the Pool capacity exceeds the threshold when a Snapshot pair is in PSUS status, the pair status changes to PFUS in the CCI. For details, please refer to the Command Control Interface (CCI) User and Reference Guide.

4. If you want to delete only snapshot data and leave Copy-on-Write Snapshot pair, use pairresync to the PSUS or PFUS pair. During the operation, the pair status changes to COPY(RS).

If you want to delete only snapshot data and leave Copy-on-Write Snapshot pair, issue the pairresync command. During the operation, the pair status changes to COPY(RS). If you want to delete the Copy-on-Write Snapshot pair, use pairsplit -S or use the Storage Navigator. During the operation, the pair status changes to SMPL(PD).

5. Use pairresync -restore on the Copy-on-Write Snapshot pair in PSUS status to restore the pair. After that, the snapshot data will be written back to the P-VOL. During the operation, the pair status changes to COPY(RS-R). When the operation completes, the pair status change to PAIR.

6. A Pool can contain only a predefined amount of data. If the total capacity of the snapshot data in the Pool exceeds the Pool capacity, the pair status changes to PSUE. The pair status changes to PSUE also when a failure occurs while restoring the pair, or when the usage rate of the Pool reaches to 100 percent. The pair status may changes to PSUE when the failure occurs during the process other than restoring.

Whether the host can read and write the P-VOL or V-VOL of a Copy-on-Write Snapshot pair depends on the status of the pair. Table 3.2 shows the relationship between the pair status and the availability of the host access.


Table 3.2 Whether Hosts can Access P-VOL and V-VOL

P-VOL V-VOL No. Pair Status

Read Write Read Write

1 SMPL OK OK - -

2 COPY OK OK No No

3 PAIR/PFUL OK OK No No

4 PSUS/PFUS OK OK OK OK

5 SMPL(PD) OK OK No No

6 COPY(RS) OK OK No No

7 COPY(RS-R) OK OK No No

8 PSUE OK* OK* No No

* If the pair status changes to PSUE because of the failure during the restoration, host cannot access that pair.

Use the Detail panel, or S-Vol Path panel, to display the Copy-on-Write Snapshot pairs detail information. In the Detail panel, you can see the information such as the Pool usage rate of a P-VOL and the snapshot IDs. Pair information such as port ID, host group ID, or LUN can be found in the S-Vol Path panel.

3.9.1 Specifying the Volumes Displayed in the Volume List

You can display only the specified volumes in the volume list if you specify the conditions in the Display Filter panel.

To display the Display Filter panel:

1. Display the ShadowImage Main panel.

2. Select the Display Filter button or right click the volume list.

If you select the Display Filter button, the Display Filter panel will be displayed. If you right click the volume list, the pop-up menu will be displayed, so go to the next step.

3. Select Display Filter from the pop-up menu.

The Display Filter panel is displayed.


Figure 3.15 Copy-on-Write Snapshot Tab of the Display Filter Panel

Note:

– For details about the ShadowImage tab of the Display Filter panel, please refer to the ShadowImage User’s Guide.

– The filter settings are only effective within the current operations in the ShadowImage Main panel. If you start another program product, or click a button on the toolbar on the Storage Navigator main panel, the settings will be reset.

If you select the check boxes in the Display Filter panel, only the volumes that meet the condition(s) are displayed in the volume list. If you deselect the check boxes, the corresponding volumes will not be displayed in the volume list.


3.10 Displaying the Copy-on-Write Snapshot Pairs Detail Information

Use the Detail panel or the S-Vol Path panel if you want to know information related to a Copy-on-Write Snapshot pair. In the Detail panel, you can see information such as the Pool usage rate of a P-VOL and the snapshot IDs. In the S-Vol Path panel, pair information such as port ID, the group number of host group or iSCSI target, or LUN can be found.

Use the History panel if you want to know the information related to the operational history of Copy-on-Write Snapshot pairs, such as creation or deletion of the pairs, and snapshot data storage statistics. See section 3.11 for details about the type of information referred from the History panel, and for general use of the panel itself.

You can display the Detail panel by first displaying the ShadowImage Main panel then right clicking on a Copy-on-Write Snapshot pair from the volume list. You can then select Detail from the menu and the Detail panel will appear, see section 2.6.4.


3.11 Displaying the Operation History

Use the History panel to display the history of the operations of Copy-on-Write Snapshot pairs such as pair creation, pair deletion, and storing snapshot data in the Pool.

To display the History panel:




3. Select the History tab.

The History panel is displayed.

Note: To update the information on the History panel, select the Refresh button.

Figure 3.16 History Panel


The upper area of the History panel lists the operation history of ShadowImage pairs, and the lower area of the panel lists the operation history of Copy-on-Write Snapshot pairs. For details about the operation history of ShadowImage pairs, refer to the ShadowImage User’s Guide. The lower area of the History panel displays the following items.

Time

The date and time (YYYY/MM/DD hour/min/sec) when a Copy-on-Write Snapshot pair or volume operation has been performed is displayed.

P-Vol

CU number and LDEV number of a P-VOL used for Copy-on-Write Snapshot operation is displayed.

S-Vol

CU number and LDEV number of a S-VOL used for Copy-on-Write Snapshot operation is displayed. When there is no S-VOL, --- will be displayed.

MU

Snapshot data ID of snapshot data used for Copy-on-Write Snapshot operation is displayed.

Pool

Pool ID of the Pool in which the Copy-on-Write Snapshot pair is registered is displayed.

Code

Reference code for Copy-on-Write Snapshot is displayed. For details on reference code, see Table 3.3.

Message

Message that indicates the operation or status of Copy-on-Write Snapshot pair is displayed. See Table 3.3.


Table 3.3 Copy-on-Write Snapshot History Reference Codes and Messages

Code Message Description

0x2001 PAIR A Copy-on-Write Snapshot pair was created.

0x2011 PSUS A Copy-on-Write Snapshot pair was split.

0x2021 SMPL A Copy-on-Write Snapshot pair was deleted.

0x2030 COPY(RS-R) START Restoration of a Copy-on-Write Snapshot pair started.

0x2031 COPY(RS-R) END Restoration of a Copy-on-Write Snapshot pair ended normally.

0x2032 COPY(RS-R) ENDED ABNORMAL Restoration of a Copy-on-Write Snapshot pair ended abnormally.

0x2051 COPY(RS) Snapshot data was deleted

0x2070 PSUE(ABNORMAL END) A failure occurred and the status of the Copy-on-Write Snapshot pair changes to PSUE.

0x2040 INITIALIZE START Initialization started.

0x2041 INITIALIZE END Initialization ended normally.

0x2042 INITIALIZE ENDED ABNORMAL Initialization ended abnormally.


Chapter 4 Troubleshooting

This chapter describes the general troubleshooting you may need when you use the Storage Navigator, and the troubleshooting for the use of the Copy-on-Write Snapshot.

4.1 General Troubleshooting

The user is responsible for the operations and usual maintenance of Storage Navigator computers. For details about general errors and the troubleshooting for those errors, please refer to the Storage Navigator™ User’s Guide.

When you operate a Storage Navigator computer, check the following:

Network and wiring

Make sure that the wiring of the computer is secure. You should check the wiring of the computer and the LAN regularly.

Rebooting of the computer

Before rebooting the computer, quit the Storage Navigator and the web browser.

Error code

For details about error codes that are displayed on the Storage Navigator computer and the measures against those errors, please refer to the Storage Navigator™ Error Codes.

Status lamp

When the status lamp of the Storage Navigator main panel is yellow or red, check the status of the disk subsystem by using the Status panel. If you cannot fix the problem, please call the Support Center.

Obtaining trace files by the FD dump tool

When the error occurred and you cannot fix the problem, get the trace file of the Storage Navigator by using the FD dump tool, and call the Support Center. For details about the FD dump tool, refer to the Storage Navigator™ User’s Guide.

106 Chapter 4 Troubleshooting

4.2 Copy-on-Write Snapshot Troubleshooting

Table 4.1 shows problems that are likely to occur when you are using Copy-on-Write Snapshot. The table also describes the causes of the problems and what you should do to solve the problems.

Table 4.1 Copy-on-Write Snapshot Troubleshooting

No. Problems Causes and Solutions

1 Cannot install Copy-on-Write Snapshot Causes: Shared memory for the V-VOL management area is not installed Shared memory is not set for the V-VOL management area Shared memory for the differential tables is not installed

Solutions: Call the Support Center and check if the shared memory for the

V-VOL management area and the differential tables is installed Call the Support Center and check if the shared memory for the

V-VOL management area is rightly set

2 Pool information is not displayed Causes: The Pool is blocked

Solutions: Implement the measures shown in section 4.2.1

3 A Pool is blocked Causes: The Pool-VOLs are blocked

Solutions: Implement the measures shown in section 4.2.1.

After the problems are solved, you need to complete the SIMs. If you keep the SIMs open, no new SIMs can be generated even if a Pool is blocked again. For details about the steps necessary to complete SIMs, please see section 4.2.2.

4 Pool usage rate exceeds the threshold Causes: Too much snapshot data is stored in the Pool The threshold of the Pool is too small

Solutions: Delete the snapshot data which is less important or delete the

old snapshot data to decrease the usage rate of the Pool. See section 3.7

Add Pool volumes to increase capacity. See section 3.2.3 Set a lager Pool threshold value. See section 3.2.4

After the problems are solved, you need to complete the SIMs. If you keep the SIMs open, no new SIMs can be generated even if the usage rate exceeds the threshold value again. For details about the steps necessary to complete SIMs, please see section 4.2.2.

Note: Only unused volumes can be added to Pool volumes. If an unused volume isn’t available, you must create new volumes, or ask the Support Center to add hard disks

5 Cannot add Pool-VOLs. Causes: Already 1,024 Pool-VOLs are set in the Pool.


No. Problems Causes and Solutions Available Pool management block in the V-VOL management

area (which is in the shared memory) is insufficient. Solutions: Add Pool-VOLs to another Pool. See section 3.2.3. Initialize the V-VOL management area. See section 3.1.3.1

6 Cannot create Copy-on-Write Snapshot pairs Causes: There are not enough differential tables to create the pairs. The conditions to create the pair are not fulfilled. The volumes specified to create the pair is in SMPL(PD) status

because the pair is being deleted. Solutions: Secure enough differential tables to create the Copy-on-Write

Snapshot pairs. See section 2.2. Fulfill the conditions to create the pair and try the pair creation

again. See section 3.5. See the ShadowImage main panel and verify that the status of

the volume changes to SMPL, and then try the pair creation again.

Execute CCI’s inqraid command and verify that the volume is not used by Copy-on-Write Snapshot, and then try the pair creation again.

7 Copy-on-Write Snapshot pairs are not displayed in the volume list

Causes: Copy-on-Write Snapshot pairs are not created Displaying of the Copy-on-Write Snapshot pairs is prohibited by

the filtering function Solutions: Create Copy-on-Write Snapshot pairs. See section 3.5 Change the settings in the Display Filter panel. See section

2.6.3.2, and section 3.9.1

8 An error occurred while restoring the pair Causes: A volume is blocked because a failure occurred in the hard disk

drive Solutions: Delete the Copy-on-Write Snapshot pair that is blocked, and call

the Support Center. For details about restoring and deleting pairs, see section 3.7

9 A volume is blocked Causes: A failure occurred in two or more hard disk drives The breaker was turned off once and then switch on the power

supply Solutions: Ask the Support Center to solve the problem

10 Trouble occurs on the application software installed in the host computer in order to monitor the volumes.

Causes: Volume access is rejected.

Solutions: Terminate the application software which monitors the volumes. Change all the Copy-on-Write Snapshot pair statuses to PSUS,

then start the application software to monitor the volumes.


No. Problems Causes and Solutions For details about the relations between the pair status and host access, see Table 3.2.

11 When the host computer tries to access the port, error occurs and the host cannot access the port

Causes: Some ports go offline because the access to the volume on the

other port(s) is rejected. Solutions: Wait for a while, then try the operation again. If the application software is installed in the host to monitor the

volume, terminate the application.

Please call the Support Center if the problem cannot be solved by the solutions offered in Table 4.1, or if the problem is not listed.


4.2.1 Recovering a Blocked Pool

When a Pool is blocked, you must recover the Pool-VOLs, Pool, Copy-on-Write Snapshot pairs, and the V-VOLs in that order. This section describes the procedure to recover the blocked Pool.

Recover the Pool-VOLs

If the Pool-VOL is blocked, please call the Support Center.

Recover the Pool




The Pool panel is displayed.

3. Select and right click the blocked Pool in the Pool tree in the Pool panel.


4. Select Restore Pool from the pop-up menu.

The restore selected Pool dialog box will appear. Select its OK button and the icon of the selected Pool will change to show normal status.

5. Select the Apply button, and select OK in the confirmation message and the restoration process will begin in the subsystem.


If there is more than one blocked Pool you may restore them all at once by following the steps below.

1. Display the Pool panel and right-click the C.O.W. Snapshot icon in the Pool tree.

2. Select Restore Pool(s) from the pop-up menu and a confirmation message pop-up appears. Select its OK button and the icon of the selected Pool will change to show normal status.

3. Select the Apply button, and select OK in the confirmation message and the restoration process will begin in the subsystem.

Using the Pool panel, you can check whether the Pool has been recovered from the blocked status and restored successfully. The blocked Pool has been restored when the Pool Information status shows Normal, of the icon in the Pool tree shows Normal status.

You can also recover the Pool by following one of these procedures.

– Add Pool-VOLs (see section 3.2.3).

– Delete snapshot data to decrease the usage rate of the Pool (see section 3.7).

– Delete snapshot data to decrease the usage rate of the pool (see section 5.7).

– Delete Snapshot pairs to decrease the usage rate of the Pool (see section 3.7).

Usage rate and status of the Pool is displayed in the Pool Information box in the Pool panel. Use these information in the box to decide how many Pool volumes to add or which snapshot data to delete.

Recover the Copy-on-Write Snapshot pair

When the Pool is blocked, the status of all Copy-on-Write Snapshot pairs that have snapshot data stored in the Pool changes to PSUE. To recover the PSUE pairs, delete those pairs. For details about deleting pairs, see section 3.7.

Recover the V-VOL

When the V-VOL is blocked, please call the Support Center.


4.2.2 Completing Pool Related Service Information Messages (SIMs)

These SIMs (Service Information Messages) will be displayed when the usage rate of the Pool exceeds its threshold, or when the Pool becomes blocked:

– Reference code 6000XX: When the usage rate of the Pool exceeds its threshold

– Reference code 6001XX: When the Pool becomes blocked

The XX’s following the numeric values display the Pool ID. Please call the Support Center for details about the SIM reference codes. You can use the Storage Navigator panel to reference the SIMs occurring in the disk subsystem.

Note: When you clear a SIM its status changes to “completed”. After the trouble that caused the SIM is solved, please complete the SIM and change its status to “completed”.

To clear these SIMs:

1. Using the Storage Navigator, identify the Pool that has exceeded its threshold value and change its status to Normal. Restore the blocked Pool to change its status to Normal. See Table 4.1 for information about solutions for Pool threshold usage rates and blocked Pools.



3. If the Storage Navigator is not already in the Modify mode, please select that mode now.


5. Select the SIM Complete Request check box, and select Apply.

6. Select OK in the confirmation message.

The confirmation message closes and the SIM complete process begins. It takes time if there are many SIMs to be completed.

You can check whether the SIMs have completed successfully using the Storage Navigator. For details, please refer to the Storage Navigator™ User’s Guide.


4.2.3 Switching Off the Power Supply

Stop the host I/O operations before you switch off the power supply while Copy-on-Write Snapshot is running. When you switch on the power supply again, Copy-on-Write Snapshot behaves differently according to whether information in the shared memory remains before and after switching off the power supply.

If information in the shared memory remains before and after switching off the power supply

If information in the shared memory remains before and after switching off the power supply, usually you can use the Pools and the Copy-on-Write Snapshot pairs that you had been using before the switch-off. However, since the disk subsystem checks the status of the Pools and the Pool volumes, if the Pool volumes are blocked at that moment, the Pool will be blocked and the status of the Copy-on-Write Snapshot pairs changes to PSUE. When this occurs, you need to recover the Pools after the switch-on. For details about recovering the Pools, see section 4.2.1.

If information in the shared memory is lost after switching off the power supply

TagmaStore USP has a battery to maintain the information in the shared memory. However, when a certain time elapses after the breaker is turned off, the battery will die and the information in the shared memory will be lost. If information in the shared memory is lost after switching off the power supply, the information about the Pools and the Copy-on-Write Snapshot pairs are erased. Therefore, you need to create the Pools and the pairs again after the switch-on.

For the information about the amount of time before the information in the shared memory is lost when the breaker is turned off, please ask the Support Center.

4.2.4 Replacing the Microprogram Offline

Usually, microprogram replacement is performed online, but in some cases, such as when the shared memory configuration needs to be changed, microprogram replacement will be performed offline. When the microprogram is replaced offline, Pool information or Snapshot pair information in the shared memory will be lost. Therefore, you must create the Pools and the pairs again after the microprogram is replaced.


Acronyms and Abbreviations

CCI Command Control Interface CU control unit (logical control unit)

DASD direct-access storage device

GB gigabyte

ID identification I/O input/output

LAN local area network LBA logical block address LDEV logical device LU logical unit LUN logical unit number, logical unit LUSE LU Size Expansion LVI logical volume image

NAS network attached storage

RCU remote control unit R-SIM remote service information message SIM service information message

SLPR storage logical partition

S-VOL secondary volume SVP service processor

USP Universal Storage Platform

VMA volume management area VOL volume

WWN worldwide name

114 Acronyms and Abbreviations

Copy on Write Snapshot

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