HUAWEI OceanStor Enterprise Unified Storage System RAID 2.0+ … · 2014-11-28 · 1.2 Introduction...

HUAWEI OceanStor Enterprise Unified Storage System

RAID 2.0+ Technical White Paper

Issue 01

Date 2014-06-04

HUAWEI TECHNOLOGIES CO., LTD.

Issue 01 (2014-06-04) Huawei Proprietary and Confidential

Copyright © Huawei Technologies Co., Ltd.

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RAID 2.0+ Technical White Paper Contents



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Contents

1 Overview ......................................................................................................................................... 1

1.1 RAID Technology Evolution ........................................................................................................................................ 1

1.2 Introduction to Huawei RAID 2.0+ .............................................................................................................................. 2

2 Working Principle ......................................................................................................................... 3

2.1 Basic Principle of RAID 2.0+ ....................................................................................................................................... 3

2.2 RAID 2.0+ Implementation Framework ....................................................................................................................... 4

2.3 Logical Objects Involved in RAID 2.0+ ....................................................................................................................... 5

3 Technical Features......................................................................................................................... 9

3.1 Secure and Trusted ........................................................................................................................................................ 9

3.1.1 Automatic Load Balancing, Decreasing the Overall Failure Rate ............................................................................. 9

3.1.2 Fast Thin Reconstruction, Reducing Dual-Disk Failure Probability ....................................................................... 10

3.1.3 Fault Detection and Self-Healing, Ensuring System Reliability .............................................................................. 12

3.2 Flexible and Efficient .................................................................................................................................................. 12

3.2.1 Pool Virtualization, Simplifying Storage Planning and Management ...................................................................... 12

3.2.2 One LUN Across More Disks, Improving Performance of a Single LUN ............................................................... 13

3.2.3 Dynamic Space Distribution, Flexibly Adapting to Service Changes...................................................................... 14

4 Configuration ............................................................................................................................... 15

4.1 Configuring RAID 2.0+ .............................................................................................................................................. 15

4.1.1 Configuring Disk Domains and Storage Pools ........................................................................................................ 15

4.1.2 Configuring LUNs and LUN Groups....................................................................................................................... 17

4.1.3 Configuring Hosts and Host Groups ........................................................................................................................ 19

4.1.4 Configuring Mapping Views .................................................................................................................................... 22

A FAQs ............................................................................................................................................. 24

B Related Resources....................................................................................................................... 27

C Acronyms and Abbreviations .................................................................................................. 28


RAID 2.0+ Technical White Paper 1 Overview



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1 Overview

1.1 RAID Technology Evolution

The term redundant array of independent disks (RAID) was first defined by the University of

California, Berkeley in 1987. The basic idea of RAID is to combine multiple independent

physical disks based on a certain algorithm to form a virtual logical disk that provides a larger

capacity, higher performance, or better data error tolerance.

As a mature and reliable data protection standard, RAID has always been used as a basic

technology by storage systems since its existence. However, with rapid growth of data storage

needs and emergence of high-performance applications in recent years, traditional RAID

gradually exposes its defects.

IDC predicts that the storage market will keep an annual growth rate of at least 10% on

average in the following five years and the global storage capacity may reach 16,840 PB. To

meet data growth requirements, disk device manufacturers keep using more advanced

technologies to increase the unit storage density of disks. Nowadays, 4 TB large-capacity

disks and 900 GB high-performance SAS disks are commonly seen in enterprise and

consumer markets. However, data reconstruction implemented upon the failure of a

large-capacity disk reveals the disadvantages of traditional RAID.

For example, traditional RAID 5 (8D+1P) needs 40 hours to reconstruct data on a 7.2k rpm 4

TB disk. The reconstruction process consumes system resources, decreasing the overall

performance of the application system. If a user restricts the reconstruction priority in return

for timely application response, the reconstruction time will be even longer. In addition,

during the time-consuming reconstruction, a large number of access operations may cause the

failure of other disks in the RAID group, greatly increasing the disk failure probability and

data loss risk.

On the other hand, traditional RAID is subject to the number of disks. In the era of soaring

data growth, traditional RAID fails to meet enterprises' needs for unified and flexible resource

scheduling. Besides, as disk capacity increases, disk-based data management becomes

increasingly inefficient.

To resolve the preceding issues of traditional RAID and follow the virtualization trend, many

storage vendors adopt substitutes for traditional RAID as follows:

LUN virtualization: Based on traditional RAID, some storage vendors such as EMC and

HDS divide RAID groups into more fine-grained units and combine these units to form

storage space accessible to hosts.

Block virtualization: Some storage vendors such as Huawei and HP 3PAR divide the

space of disks that belong to a storage pool into small-granularity data blocks and create


RAID 2.0+ Technical White Paper 1 Overview



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RAID groups based on these data blocks. This approach allows data to be evenly

distributed onto all disks in the storage pool and enables resources to be managed in the

form of data blocks.

Figure 1-1 RAID technology evolution

1.2 Introduction to Huawei RAID 2.0+

HUAWEI OceanStor enterprise unified storage systems are brand-new storage systems

designed based on the current application status of storage products and storage technology

trends. Featured by virtualization, hybrid cloud, thin IT, and low carbon, they are intended for

medium- and large-sized data centers and focus on the core services of medium- and

large-sized enterprises.

OceanStor enterprise unified storage systems employ an innovative Smart Matrix

all-switching hardware architecture. With the use of a dedicated storage operating system

called eXtreme Virtual Engine (XVE), OceanStor enterprise unified storage systems meet

various storage requirements of large-sized data centers.

RAID 2.0+ is a brand-new RAID technology developed by Huawei to overcome the

disadvantages of traditional RAID and keep in line with the storage architecture virtualization

trend. RAID 2.0+ implements two-layer virtualized management instead of the traditional

fixed management. Based on underlying disk management that employs block virtualization

(Virtual for Disk), RAID 2.0+ uses Smart series efficiency improvement software to

implement efficient resource management that features upper-layer virtualization (Virtual for

Pool).


RAID 2.0+ Technical White Paper 2 Working Principle



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2 Working Principle

2.1 Basic Principle of RAID 2.0+

Huawei RAID 2.0+ employs two-layer virtualized management, namely, underlying disk

management plus upper-layer resource management. In a storage system, the space of each

disk is divided into data blocks with a small granularity, and RAID groups are created based

on data blocks so that data is evenly distributed onto all disks in a storage pool. Besides, using

data blocks as the smallest units greatly improves the efficiency of resource management.

1. OceanStor enterprise unified storage systems support SSDs, SAS disks, and NL-SAS

disks, which compose disk domains. In a disk domain, disks of the same type compose

disk groups (DGs) based on certain rules.

2. The space of each disk in a DG is divided into chunks (CKs) of a fixed size. OceanStor

enterprise unified storage systems select chunks from different disks at random to

compose chunk groups (CKGs) based on a certain RAID algorithm.

3. Each CKG is divided into logical storage spaces of a fixed size called extents. Extents

are the basic units that compose thick LUNs (also called fat LUNs). In terms of thin

LUNs, extents are further divided into grains that have a smaller granularity, and grains

are mapped to thin LUNs.





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2.2 RAID 2.0+ Implementation Framework

The following figure shows the implementation framework of RAID 2.0+ employed by

OceanStor enterprise unified storage systems.

A disk domain in OceanStor enterprise unified storage systems consists of disks from

one or multiple storage tiers. Each storage tier supports disks of a specific type: SSDs

compose the high-performance tier, SAS disks compose the performance tier, and

NL-SAS disks compose the capacity tier.

The disks on each storage tier are divided into CKs with a fixed size of 64 MB.

CKs on each storage tier compose CKGs based on a user-defined RAID policy. Users are

allowed to define a specific RAID policy for each storage tier of a storage pool.

OceanStor enterprise unified storage systems divide CKGs into small-sized extents. An

extent is the smallest granularity for data migration and is the basic unit of a thick LUN.

When creating a storage pool, users can set the extent size on the Advanced page. The

default extent size is 4 MB.

Multiple extents compose a volume that is externally presented as a LUN (which is a

thick LUN) accessible to hosts. A LUN implements space application, space release, and

data migration based on extents. For example, when creating a LUN, a user can specify a

storage tier from which the capacity of the LUN comes. In this case, the LUN consists of

the extents on the specified storage tier. After services start running, the storage system

migrates data among the storage tiers based on data activity levels and data migration

polices. (This function requires a SmartTier license.) In this scenario, data on the LUN is

distributed to the storage tiers of the storage pool based on extents.





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When a user creates a thin LUN, OceanStor enterprise unified storage systems divide

extents into grains and map grains to the thin LUN. In this way, fine-grained

management of storage capacity is implemented.

2.3 Logical Objects Involved in RAID 2.0+

This section describes the major logical objects and key concepts related to RAID 2.0+.

Disk Domain

A disk domain is a combination of multiple disks (or all the disks of a storage system). After

disks are consolidated and a certain amount of hot spare space is reserved, a disk domain

provides storage resources for storage pools in a unified manner.

One or more disk domains can be created in an OceanStor enterprise unified storage

system.

Multiple storage pools can be created in a disk domain.

A disk domain can consist of SSDs, SAS disks, or NL-SAS disks.

Disk domains are isolated from one another, including performance, storage resources,

and faults.

Storage Pool and Tier

A storage pool is a storage resource container. The storage resources used by application

servers are all from storage pools. Created based on a specific disk domain, a storage pool

dynamically allocates CK resources of the disk domain and enables these CKs to compose

CKGs based on the RAID policy defined for each storage tier. Then, the CKGs provide

applications with storage resources that have RAID protection.

A storage tier is a collection of storage media providing the same level of performance in a

storage pool. Different storage tiers manage storage media with different performance levels

and provide storage space for applications that have different performance requirements.

Based on disk types, a storage pool can be divided into multiple tiers. The following table

describes the storage tiers and disk types supported by OceanStor enterprise unified storage

systems.

Storage Tier

Tier Name Supported Type of Disks

Application

Tier 0 High-perfor

mance tier

SSD SSDs provide high performance but are

expensive. Therefore, SSDs are

suitable for storing data most

frequently accessed.

Tier 1 Performance

tier

SAS SAS disks provide moderate

performance and are inexpensive.

Therefore, SAS disks are suitable for

storing data less frequently accessed.





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Storage Tier

Tier Name Supported Type of Disks

Application

Tier 2 Capacity tier NL-SAS NL-SAS disks provide low

performance but a large capacity per

disk at a low cost. Therefore, NL-SAS

disks are suitable for storing a large

amount of data that is seldom accessed.

When creating a storage pool, a user is allowed to specify storage tiers allocated from the

corresponding disk domain and define a RAID policy and a capacity for each tier.

OceanStor enterprise unified storage systems support RAID 5, RAID 6, and RAID 10.

The following table lists the supported RAID policies.

RAID Level RAID Policy

RAID 5 4D+1P, 8D+1P

RAID 6 4D+2P, 8D+2P

RAID 10 2D+2D or 4D+4D, which is automatically selected

by storage systems

The capacity tier consists of large-capacity NL-SAS disks. It is recommended that RAID

6 (a double-parity RAID level) be used as the RAID policy for this tier.

Disk Group (DG)

A DG is a group of disks of the same type and from the same disk domain. There are three

disk types: SSD, SAS, and NL-SAS. Based on the number of disks of each type in each disk

domain, OceanStor enterprise unified storage systems automatically allocate disks to one or

more DGs.

One DG consists of disks of only one type.

CKs in a CKG come from different disks that belong to the same DG.

DGs are internal objects automatically configured by OceanStor enterprise unified

storage systems and typically used for fault isolation. DGs are not presented externally.

Logical Drive (LD)

LDs are logical disks managed by an OceanStor enterprise unified storage system. Each LD

corresponds to a physical disk.





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CK

Each CK is 64 MB physical space divided from disk space in a storage pool. CK is the basic

unit of a RAID group.

CKG

A CKG is a logical storage unit that consists of CKs from different disks in the same DG

based on a RAID algorithm. A storage pool allocates resources from a disk domain by taking

CKG as the smallest unit.

All CKs in a CKG come from disks in the same DG.

A CKG has RAID properties, which are configured for the corresponding storage tier.

CKs and CKGs are internal objects automatically configured by OceanStor enterprise

unified storage systems. They are not presented externally.

Extent

An extent is a logical storage space with a fixed size divided from a CKG. The size ranges

from 512 KB to 64 MB. The default size is 4 MB. Extent is the smallest unit (granularity) for

data migration and hotspot data statistics collection. It is also the smallest unit for space

application and release in a storage pool.

One extent belongs to one volume or LUN.

A user can set the extent size while creating a storage pool. After that, the extent size

cannot be changed.

Extents in one storage pool may have a different size from those in another storage pool.

However, the extents in the same storage pool have the same size.





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Grain

In thin LUN mode, extents are divided into 64 KB grains. A thin LUN allocates storage space

by grains. Logical block addresses (LBAs) in a grain are consecutive.

Grains are mapped to thin LUNs. A thick LUN does not involve grains.

Volume and LUN

A volume is an internal management object in OceanStor enterprise unified storage systems.

A volume organizes all extents and grains of a LUN and applies for and releases extents to

increase and decrease the actual space occupied by the volume.

A LUN is a storage unit that can be directly mapped to a host for data read and write. A LUN

is the external display of a volume.


RAID 2.0+ Technical White Paper 3 Technical Features



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3 Technical Features

Based on two-layer virtualized management, RAID 2.0+ overcomes the inherent defects of

traditional RAID and greatly improves storage system reliability and resource management

efficiency. By leveraging RAID 2.0+, OceanStor enterprise unified storage systems provide

truly secure, trusted, flexible, and efficient enterprise storage. This chapter describes the

technical features of RAID 2.0+ in terms of secure, trusted, flexible, and efficient.

3.1 Secure and Trusted

3.1.1 Automatic Load Balancing, Decreasing the Overall Failure Rate

A traditional RAID-based storage system typically contains multiple RAID groups, each of

which consists of up to 10-odd disks. RAID groups work under different loads, leading to an

unbalanced load and existence of hotspot disks. According to the statistics collected by

Storage Networking Industry Association (SNIA), hotspot disks are more vulnerable to

failures. In the following figure, Duty Cycle indicates the percentage of disk working time to

total disk power-on time, and ARF indicates the annual failure rate. It can be inferred that

when the duty cycle is high, the ARF is almost 1.5 to 2 times higher than that in low duty

cycle scenarios.

RAID 2.0+ implements block virtualization to enable data to be automatically and evenly

distributed onto all disks in a storage pool, preventing unbalanced loads. This approach

decreases the overall failure rate of a storage system.





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3.1.2 Fast Thin Reconstruction, Reducing Dual-Disk Failure Probability

In the recent 10 years of disk development, disk capacity growth outpaces performance

improvement. Nowadays, 4 TB disks are commonly seen in enterprise and consumer markets.

5 TB disks will come into being in the second quarter of 2014. Besides, even

high-performance SAS disks specific to the enterprise market can provide up to 1.2 TB per

disk.

Rapid capacity growth confronts traditional RAID with a serious issue: reconstruction of a

single disk, which required only dozens of minutes 10 years ago, now requires 10-odd hours

or even dozens of hours. The increasingly longer reconstruction time leads to the following

problem: A storage system that encounters a disk failure must stay in the degraded state

without error tolerance for a long time, exposed to a serious data loss risk. It is common that

data loss occurs in a storage system under the dual stress imposed by services and data

reconstruction.

Based on underlying block virtualization, RAID 2.0+ overcomes the performance bottleneck

seen in target disks (hot spare disks) that are used by traditional RAID for data reconstruction.

As a result, the write bandwidth provided for reconstructed data flows is no longer a

reconstruction speed bottleneck, greatly accelerating reconstruction, decreasing dual-disk

failure probability, and improving storage system reliability.

The following figure compares the reconstruction principle of traditional RAID with that of

RAID 2.0+.

In the schematic diagram of traditional RAID, HDDs 0 to 4 compose a RAID 5 group,

and HDD 5 serves as a hot spare disk. If HDD 1 fails, an XOR algorithm is used to

reconstruct data based on HDDs 0, 2, 3, and 4, and the reconstructed data is written onto

HDD 5.

In the schematic diagram of RAID 2.0 +, if HDD 1 fails, its data is reconstructed based

on the CK granularity, where only the allocated CKs ( and in the figure)

are reconstructed. All disks in the storage pool participate in the reconstruction. The

reconstructed data is distributed on multiple disks (HDDs 4 and 9 in the figure).





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RAID 2.0+ fined-grained and efficient fault handling also contributes to reconstruction

acceleration. In addition to the original bad sector repair and disk failure reconstruction,

RAID 2.0+ provides bad block repair that only reconstructs used space based on the CK

granularity. By efficiently identifying used space, RAID 2.0+ implements thin reconstruction

upon a disk failure to further shorten the reconstruction time, mitigating data loss risks.

With great advantages in reconstruction, RAID 2.0+ enables OceanStor enterprise unified

storage systems to outperform traditional storage systems in terms of reconstruction. The

following figure compares the time that a traditional storage system and an OceanStor

enterprise unified storage system spend in reconstructing 1 TB data in an NL-SAS

large-capacity disk environment.





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3.1.3 Fault Detection and Self-Healing, Ensuring System Reliability

OceanStor enterprise unified storage systems employ a multi-level error tolerance design for

disks and provide various measures to ensure reliability, including online disk diagnosis, disk

health analyzer (DHA), bad sector background scanning, and bad sector repair. Based on a hot

spare policy, RAID 2.0+ automatically reserves a certain amount of hot spare space in a disk

domain. If an OceanStor enterprise unified storage system detects an uncorrectable media

error in an area of a disk or finds that an entire disk fails, the OceanStor enterprise unified

storage system automatically reconstructs the affected data blocks and writes the

reconstructed data to the hot spare space of other disks, implementing quick self-healing.

Traditional RAID RAID 2.0+

Independent global or local hot spare disks

must be manually configured.

Distributed hot spare space is provided

automatically.

Many-to-one reconstruction is implemented.

Reconstructed data flows are written to a

single hot spare disk in serial.

Many-to-many reconstruction is

implemented. Reconstructed data flows

are written to multiple disks in parallel.

Hotspot disks exist. The reconstruction time is

long.

Load balancing is implemented. The

reconstruction time is short.

3.2 Flexible and Efficient

3.2.1 Pool Virtualization, Simplifying Storage Planning and Management

Nowadays, mainstream storage systems typically contain hundreds of or even thousands of

disks of different types. If such storage systems employ traditional RAID, administrators need

to manage a lot of RAID groups and must carefully plan performance and capacity for each

application and RAID group. In the era of constant changes, it is almost impossible to

accurately predict the service development trends in the IT system lifecycle and the

corresponding data growth amount. As a result, administrators often face management issues

such as uneven allocation of storage resources. These issues greatly increase management

complexity.





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OceanStor enterprise unified storage systems employ advanced virtualization technologies to

manage storage resources in the form of storage pools. Administrators only need to maintain a

few storage pools. All RAID configurations are automatically completed during the creation

of storage pools. In addition, OceanStor enterprise unified storage systems automatically

manage and schedule system resources in a smart way based on user-defined policies,

significantly simplifying storage planning and management.

3.2.2 One LUN Across More Disks, Improving Performance of a Single LUN

Since the 21st century, server computing capabilities have improved greatly and the number

of host applications (such as databases and virtual machines) has increased sharply, causing

the needs for higher storage performance, capacity, and flexibility. Restricted by the number

of disks, a traditional RAID group provides only a small capacity, moderate performance, and

poor scalability. These disadvantages prevent traditional RAID groups from meeting service

requirements. When a host accesses a LUN intensively, only a limited number of disks are

actually accessed, easily causing disk access bottlenecks and making the disks hotspots.

RAID 2.0+ supports a storage pool that consists of dozens of or even hundreds of disks.

LUNs are created based on a storage pool, thereby no longer subject to the limited number of

disks supported by a RAID group. The wide striping technology distributes data of a single

LUN onto many disks, preventing disks from becoming hotspots and enabling the

performance and capacity of a single LUN to improve significantly. If the capacity of an

existing storage system does not meet the needs, a user can dynamically expand the capacity

of a storage pool and that of a LUN by simply adding disks to disk domains. This approach

improves disk capacity utilization.





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3.2.3 Dynamic Space Distribution, Flexibly Adapting to Service Changes

RAID 2.0+ is implemented based on industry-leading block virtualization. Data and service

loads in a volume are automatically and evenly distributed onto all physical disks in a storage

pool. By leveraging Smart series efficiency improvement software, OceanStor enterprise

unified storage systems automatically schedule resources in a smart way based on factors such

as the amount of hot and cold data and the performance and capacity required by a service. In

this way, OceanStor enterprise unified storage systems adapt to rapid changes in enterprise

services.


RAID 2.0+ Technical White Paper 4 Configuration



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4 Configuration

This chapter describes RAID 2.0+ configuration and configuration management.

4.1 Configuring RAID 2.0+

You can configure RAID 2.0+ in the resource allocation flowchart of OceanStor

DeviceManager.

4.1.1 Configuring Disk Domains and Storage Pools

A disk domain in OceanStor enterprise unified storage systems consists of disks from one or

multiple storage tiers. A storage pool provides available storage space for users. The following

describes how to configure disk domains and storage pools in the resource allocation

flowchart.

Click Create Disk Domain. In the dialog box that is displayed, add description about the

created disk domain. You can select the number and type of available disks for the disk

domain. Then click OK.





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Click Create Storage Pool. In the dialog box that is displayed, add description about the

created storage pool. You can select the disk domain to which the storage pool belongs

and a disk type and RAID policy for the storage pool. Then enter the capacity of the

storage pool. In the Advanced Property Settings dialog box that is displayed, set

Capacity Alarm Threshold and Data Migration Granularity. Then click OK.

4.1.2 Configuring LUNs and LUN Groups

You can configure LUNs and LUN groups only after disk domains and storage pools are

configured. LUNs are the units provided for users to store data. A LUN group consists of

multiple LUNs. A LUN can be detected only when the LUN belongs to a LUN group.





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Click Create LUN. In the dialog box that is displayed, add description about the created

LUN. You can set the LUN capacity, the number of LUNs to be created, and the storage

pool to which the LUN belongs. In the Advanced dialog box, you can set the owning

controller for the LUN and related policies (you can use the default settings if there are

no special requirements). Then click OK.

Click Create LUN Group. In the dialog box that is displayed, add description about the

created LUN group and add all or part of created LUNs into the LUN group. Then click

OK.





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4.1.3 Configuring Hosts and Host Groups

To smoothly read and write a LUN, you must configure a host that reads and writes the LUN

and set up a communication channel from the host to the storage system.

Click Create Host. In the dialog box that is displayed, add description about the created host,

including the host name and host operating system and ensure that a communication link

exists between the host and storage system. You can leave IP Address blank and enter the

device location. Then click Next.





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In the Configure the Initiator dialog box, add an initiator for the host. Then repeatedly

click Next until the procedure ends.

Click Create Host Group. In the dialog box that is displayed, add the created host into

the host group. Then click OK.





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4.1.4 Configuring Mapping Views

After the previous configurations, configured LUNs must be presented to the host. Therefore,

a mapping view must be configured.

Click Create Mapping View. In the dialog box that is displayed, add description about

the created mapping view. Select the LUN group and host group that you want to add to

the mapping view. Then click OK.





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RAID 2.0+ Technical White Paper A FAQs



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A FAQs

Q1. Must all disks of an OceanStor enterprise unified storage system reside in the same

storage pool?

Answer: No. An OceanStor enterprise unified storage system manages disks based on disk

domains and storage pools. A user can create one or more disk domains that are isolated from

one another in terms of resources, performance, and faults. One or more storage pools can be

created in a disk domain. Each storage pool uses various types of disks to provide storage

space.

Q2. How does an OceanStor enterprise unified storage system treat data in the event of

capacity expansion and disk failure?

Answer: After a disk is added to a storage pool, the OceanStor enterprise unified storage

system automatically moves a certain amount of data to the newly added disk space based on

disk usage for capacity balancing so that all disks in the same storage pool have similar space

utilization.

If a disk fails, CKGs related to the failed disk automatically perform data reconstruction, and

the reconstructed data is evenly written to the hot spare space of other functional disks. Users

do not need to specify hot spare space. The OceanStor enterprise unified storage system

automatically selects hot spare space based on disk usage. For details about the reconstruction

process, see section 3.1.2 "Fast Thin Reconstruction, Reducing Dual-Disk Failure

Probability."

Q3. Compared with traditional RAID, in what aspects does RAID 2.0+ demonstrate its high

reliability?

Answer: RAID 2.0+ demonstrates its high reliability in the following aspects:

Load balancing: RAID 2.0+ enables disks to work in a balanced manner, preventing

some disks from being overstressed, which may occur in traditional RAID. For details,

see section 3.1.1 "Automatic Load Balancing, Decreasing the Overall Failure Rate."

Robust reconstruction: RAID 2.0+ enables more disks to share reconstruction loads,

reducing the work stress on each disk. In this way, the disk failure risk is minimized

during reconstruction.

Rapid reconstruction: RAID 2.0+ significantly shortens the reconstruction window to

help an OceanStor enterprise unified storage system regain the error tolerance capability

as soon as possible, thereby improving system reliability. For details, see section 3.1.2

"Fast Thin Reconstruction, Reducing Dual-Disk Failure Probability."





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Thin reconstruction: Based on metadata, RAID 2.0+ detects allocated space in use. In the

event of reconstruction, RAID 2.0+ reconstructs only the used space to reduce the

workload and shorten the reconstruction time, lowering the reconstruction failure risk.

Self-healing: RAID 2.0+ uses distributed hot spare space. If an OceanStor enterprise

unified storage system detects a fault, reconstruction automatically starts as long as there

are free CKs in disks, thereby improving reliability and cutting management costs. For

details, see section 3.1.3 "Fault Detection and Self-Healing, Ensuring System

Reliability."

Minimized data loss amount: If a traditional RAID group fails, all data in the RAID

group is affected. In terms of RAID 2.0+, if multiple disks fail, only the data related to

these failed disks is affected, and other data is still accessible. Therefore, the amount of

lost data is much less.

Based on the Markov model, the following table lists the data loss risks of traditional RAID

and RAID 2.0+, with data loss probability and data loss amount taken into consideration.

System Configuration

RAID 2.0+ Configuration

Traditional RAID Configuration

Data Loss Risk

(Traditional RAID/RAID 2.0+)

40 x 600 GB

SAS disks

(disk failure

rate: 1%)

RAID 5 (4+1 disks), 40

disks per DG

Eight RAID 5

(4+1 disks)

groups

16.09

40 x 2 TB

SATA disks

(disk failure

rate: 2%)

RAID 6 (8+2 disks), 40

disks per DG

Four RAID 6

(8+2 disks)

groups

69.29

40 x 600 GB

SAS disks

(disk failure

rate: 1%)

RAID 10 (10 disks), 40

disks per DG

Four RAID 10

(10 disks) groups

39.15

Q4. Is disk utilization of OceanStor enterprise unified storage systems low?

Answer: OceanStor enterprise unified storage systems employ a two-layer virtualization

software architecture based on RAID 2.0+. To flexibly and efficiently manage data, certain

capacity is reserved. However, some people ignore the storage efficiency and think the disk

utilization is low due to the capacity reservation. With this innovative architecture, Huawei

storage delivers the highest storage efficiency in the industry. For example, block-based

resource management ensures global load balancing and improves the reconstruction speed by

20 times. The upper-layer virtualization leverages Smart series software to allocate system

resources in a smart way, notably improving resource utilization.

If SAS disks are used to create RAID 5 (8D+1P) groups, the capacity utilization is about

83.42%, which is 5% lower than the capacity utilization of traditional RAID.

Q5. Will data be lost if two disks concurrently fail in an OceanStor enterprise unified storage

system?

Answer: The essence of this question is about the error tolerance capability of RAID. RAID is

the basis of data storage protection. RAID 5 tolerates a concurrent failure of only one disk (for





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traditional RAID) or CK (for RAID 2.0+). RAID 6 tolerates a concurrent failure of two disks

or CKs. Therefore, if you employ a double-parity RAID level (such as RAID 6) regardless of

traditional RAID or RAID 2.0+, a concurrent failure of two disks will not cause data loss.

If RAID 5 is employed, a concurrent failure of two disks will cause data loss in traditional

RAID scenarios. For an OceanStor enterprise unified storage system that employs RAID 2.0+,

however, as long as each CKG does not contain two failed CKs, data will not be lost.

The following figure shows a storage pool that consists of 20 disks, where storage space is

provided for hosts in the form of LUNs, and the RAID policy is RAID 5 (4D+1P).

If HDDs 7 and 9 concurrently fail, only CKs related to the two disks are affected. In the

preceding figure, CKs 71 to 76 and CKs 101 to 106 are affected, whereas CKs 77 to 79 and

CKs 107 to 109 are not affected because no data is stored in these idle CKs. Accordingly,

CKGs 0, 1, 2, 4, 8, 11, 12, 13, 17, 19, 21, and 23 (the red CKGs with an underscore) are

affected. CKGs adopt the RAID 5 (4D+1P) policy, and each affected CKG contains only one

failed CK. Therefore, data provided by each of these CKGs is still available. In terms of hosts,

the corresponding LUNs are still accessible and services are not interrupted.


RAID 2.0+ Technical White Paper B Related Resources



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B Related Resources

1. RAID 2.0+ Technology Video, helping you easily learn about the advantages and

principles of RAID 2.0+

http://3ms.huawei.com/mm/video/videoMaintain.do?method=showVideoDetail&f_id=142196

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2. Logical Objects and Key Concepts Related to RAID 2.0+

http://3ms.huawei.com/mm/docMaintain/mmMaintain.do?method=showMMDetail&f_id=ST

R13072905120079

http://3ms.huawei.com/mm/docMaintain/mmMaintain.do?method=showMMDetail&f_id=ST

R13072425080025



http://3ms.huawei.com/mm/docMaintain/mmMaintain.do?method=showMMDetail&f_id=STR13072905120079





RAID 2.0+ Technical White Paper C Acronyms and Abbreviations



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C Acronyms and Abbreviations

Table 4-1 Acronyms and abbreviations

Acronym and Abbreviation Full Spelling

RAID redundant array of independent disks

RPM Revolutions Per Minute

LUN logical unit number

RAID eXtreme Virtual Engine

XVE Chunk

CK Chunk Group

CKG Disk Group

DG Logical Drive

LD Storage Networking Industry Association

SNIA Annual Failure Rate

AFR Disk Health Analyzer

DHA redundant array of independent disks

HUAWEI OceanStor Enterprise Unified Storage System RAID 2.0+ … · 2014-11-28 · 1.2 Introduction...

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