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Transcript of © 2006 EMC Corporation. All rights reserved. Business Continuity: Remote Replication Module 4.4.
© 2006 EMC Corporation. All rights reserved.
Business Continuity: Remote ReplicationBusiness Continuity: Remote Replication
Module 4.4
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 2
Remote Replication
After completing this module, you will be able to:
Explain Remote Replication Concepts– Synchronous/Asynchronous
– Connectivity Options
Discuss Host and Array based Remote Replication Technologies– Functionality
– Differences
– Considerations
– Selecting the appropriate technology
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 3
Remote Replication Concepts
Replica is available at a remote facility– Could be a few miles away or half way around the world
– Backup and Vaulting are not considered remote replication
Synchronous Replication– Replica is identical to source at all times – Zero RPO
Asynchronous Replication– Replica is behind the source by a finite margin – Small RPO
Connectivity– Network infrastructure over which data is transported from source
site to remote site
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 4
Synchronous Replication
A write has to be secured on the remote replica and the source before it is acknowledged to the host
Ensures that the source and remote replica have identical data at all times– Write ordering is maintained at all times
Replica receives writes in exactly the same order as the source
Synchronous replication provides the lowest RPO and RTO– Goal is zero RPO
– RTO is as small as the time it takes to start application on the remote site
1
3
4
2Data Write
Data Acknowledgement
Server
Disk
Disk
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 5
Synchronous Replication
Response Time Extension– Application response time will be
extended due to synchronous replication Data must be transmitted to remote
site before write can be acknowledged Time to transmit will depend on
distance and bandwidth
Bandwidth– To minimize impact on response
time, sufficient bandwidth must be provided for at all times
Rarely deployed beyond 200 km
Average
Time
WritesMB/s
Max
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 6
Asynchronous Replication
Write is acknowledged to host as soon as it is received by the source
Data is buffered and sent to remote– Some vendors maintain write ordering– Other vendors do not maintain write
ordering, but ensure that the replica will always be a consistent re-startable image
Finite RPO– Replica will be behind the Source by
a finite amount– Typically configurable
1
4
2
3Data Write
Data Acknowledgement
Server
Disk
Disk
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 7
Asynchronous Replication
Response Time unaffected
Bandwidth– Need sufficient bandwidth on
average
Buffers– Need sufficient buffers
Can be deployed over long distances
Average
Time
WritesMB/s
Max
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 8
Remote Replication Technologies
Host based– Logical Volume Manager (LVM)
Synchronous/Asynchronous
– Log Shipping
Storage Array based– Synchronous
– Asynchronous
– Disk Buffered - Consistent PITs Combination of Local and Remote Replication
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 9
LVM Based Remote Replication
NetworkVolume Group
Physical Volume 1
Physical Volume 2
Physical Volume 3
Physical Volume 1
Physical Volume 2
Physical Volume 3
Local Site Remote Site
Volume Group
Log Log
Duplicate Volume Groups at local and remote sites
All writes to the source Volume Group are replicated to the remote Volume Group by the LVM– Synchronous or Asynchronous
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 10
LVM Based Remote Replication
In the event of a network failure– Writes are queued in the log file
– When the issue is resolved the queued writes are sent over to the remote
– The maximum size of the log file determines the length of outage that can be withstood
In the event of a failure at the source site, production operations can be transferred to the remote site
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 11
LVM Based Remote Replication
Advantages– Different storage arrays and RAID protection can be used at the
source and remote sites
– Standard IP network can be used for replication
– Response time issue can be eliminated with asynchronous mode, with extended RPO
Disadvantages– Extended network outages require large log files
– CPU overhead on host For maintaining and shipping log files
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 12
Host Based Log Shipping
Offered by most DB Vendors
Advantages– Minimal CPU overhead
– Low bandwidth
– Standby Database consistent
to last applied log
Original
Logs
Stand By
Logs
IP Network
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 13
Array Based – Remote Replication
Replication performed by the Array Operating Environment– Host CPU resources can be devoted to production operations
instead of replication operations
– Arrays communicate with each other via dedicated channels ESCON, Fibre Channel or Gigabit Ethernet
Replicas are on different arrays– Primarily used for DR purposes
– Can also be used for other BC operationsProduction Array Remote Array
DistanceSource Replica
Network
DR ServerProduction
Server
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 14
Array Based – Synchronous Replication
Network links
Write is received by the source array from host/server
Write is transmitted by source array to the remote array
Remote array sends acknowledgement to the source array
Source array signals write complete to host/server
Source Target
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 15
Array Based – Asynchronous Replication
No impact on response time Extended distances between arrays Lower bandwidth as compared to Synchronous
Network links
Write is received by the source array from host/server
Write is transmitted by source array to the remote array
Source array signals write complete to host/server
Remote array sends acknowledgement to the source array
Source Target
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 16
Array Based – Asynchronous Replication
Ensuring Consistency– Maintain write ordering
Some vendors attach a time stamp and sequence number with each of the writes, then ship the writes to the remote array and apply the writes to the remote devices in the exact order based on the time stamp and sequence numbers
Remote array applies the writes in the exact order they were received, just like synchronous
– Dependent write consistency Some vendors buffer the writes in the cache of the source array for a
period of time (between 5 and 30 seconds) At the end of this time the current buffer is closed in a consistent manner
and the buffer is switched, new writes are received in the new buffer The closed buffer is then transmitted to the remote array Remote replica will contain a consistent, re-startable image on the
application
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 17
Array based – Disk Buffered Consistent PITs
Local and Remote replication technologies can be combined to create consistent PIT copies of data on remote arrays
RPO usually in the order of hours
Lower Bandwidth requirements
Extended distance solution
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 18
Extended Distance Consistent PIT
Create a Consistent PIT Local Replica on Source Array Create a Remote Replica of this Local Replica Optionally create another replica of the Remote replica on the
remote array if needed Repeat…as automation, link bandwidth, change rate permit
SOURCE REMOTE
Network Links
Remote Replica
Local Replica
Local Replica
Source
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 19
Synchronous + Extended Distance Consistent PIT
Synchronous replication between the Source and Bunker Site
Create consistent PIT Local Replica at bunker Create Remote Replica of bunker Local Replica Optionally create additional Local Replica at Target site
from the Remote Replica if needed Repeat…as automation, link bandwidth, change rate
permit
SOURCE REMOTEBUNKER
SyncSource
Remote Replica
Local Replica
Local Replica
Remote Replica
Network Links
Network Links
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 20
Remote Replicas – Tracking Changes
Remote replicas can be used for BC Operations– Typically remote replication operations will be suspended when the
remote replicas are used for BC Operations
During BC Operations changes will/could happen to both the source and remote replicas– Most remote replication technologies have the ability to track
changes made to the source and remote replicas to allow for incremental re-synchronization
– Resuming remote replication operations will require re-synchronization between the source and replica
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 21
Primary Site Failure – Operations at Remote Site
Remote replicas are typically not available for use while the replication session is in progress
In the event of a primary site failure the replicas have to be made accessible for use
Create a local replica of the remote devices at the remote site
Start operations at the Remote site– No remote protection while primary site issues are resolved
After issue resolution at Primary Site– Stop activities at remote site– Restore latest data from remote devices to source– Resume operations at Primary (Source) Site
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 22
Array Based – Which Technology?
Synchronous– Is a must if zero RPO is required– Need sufficient bandwidth at all times– Application response time elongation will prevent extended distance
solutions (rarely above 125 miles)
Asynchronous– Extended distance solutions with minimal RPO (order of minutes)– No Response time elongation– Generally requires lower Bandwidth than synchronous– Must design with adequate cache/buffer or sidefile/logfile capacity
Disk Buffered Consistent PITs– Extended distance solution with RPO in the order of hours– Generally lower bandwidth than synchronous or asynchronous
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 23
Storage Array Based – Remote Replication
Network Options– Most vendors support ESCON or Fibre Channel adapters for remote
replication Can connect to any optical or IP networks with appropriate protocol
converters for extended distances DWDM SONET IP Networks
– Some Vendors have native Gigabit Ethernet adapters which allows the array to be connected directly to IP Networks without the need for protocol converters
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 24
Dense Wavelength Division Multiplexing (DWDM)
DWDM is a technology that puts data from different sources together on an optical fiber with each signal carried on its own separate light wavelength (commonly referred to as a lambda or ).
Up to 32 protected and 64 unprotected separate wavelengths of data can be multiplexed into a light stream transmitted on a single optical fiber.
ESCON
Fibre Channel
Gigabit Ethernet
Optical Channels
Optical ElectricalOptical
Lambda λ
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 25
Synchronous Optical Network (SONET)
SONET is Time Division Multiplexing (TDM) technology where traffic from multiple subscribers is multiplexed together and sent out onto the SONET ring as an optical signal
Synchronous Digital Hierarchy (SDH) similar to SONET but is the European standard
SONET/SDH, offers the ability to service multiple locations, its reliability/availability, automatic protection switching, and restoration
SONET
OC3 OC48
OC48
SDH
STM-1 STM-16
STM-16
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 26
Rated Bandwidth
Link Bandwidth Mb/s
Escon 200
Fibre Channel 1024 or 2048
Gigabit Ethernet 1024
T1 1.5
T3 45
E1 2
E3 34
OC1 51.8
OC3/STM1 155.5
OC12/STM4 622.08
OC48/STM16 2488.0
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 27
Module Summary
Key points covered in this module:
Remote Replication Concepts– Synchronous/Asynchronous
– Connectivity Options
Host and Array based Remote Replication Technologies– Functionality
– Differences
– Considerations
– Selecting the appropriate technology
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 28
Check Your Knowledge
What is a Remote Replica?
What are the possible uses of Remote Replicas?
What is the difference between Synchronous and Asynchronous Replication?
Discuss one host based remote replication technology?
Discuss one array based remote replication technology?
What are differences in the bandwidth requirements between the array remote replication technologies discussed in this module?
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 29
Apply Your Knowledge…
Upon completion of this topic, you will be able to:
Enumerate EMC’s Remote Replication Solutions for the Symmetrix and CLARiiON arrays
Describe EMC’s SRDF/Synchronous Replication Solution
Describe EMC’s MirrorView/A Replication Solution
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 30
EMC – Remote Replication Solutions
EMC Symmetrix Arrays– EMC SRDF/Synchronous
– EMC SRDF/Asynchronous
– EMC SRDF/Automated Replication
EMC CLARiiON Arrays– EMC MirrorView/Synchronous
– EMC MirrorView/Asynchronous
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 31
EMC SRDF/Synchronous - Introduction
Array based Synchronous Remote Replication technology for EMC Symmetrix Storage Arrays– Facility for maintaining real-time physically separate mirrors of
selected volumes
SRDF/Synchronous uses special Symmetrix devices– Source arrays have SRDF R1 devices– Target arrays have SRDF R2 devices– Data written to R1 devices are replicated to R2 devices
SRDF uses dedicated channels to send data from source to target array– ESCON, Fibre Channel or Gigabit Ethernet are supported
SRDF is available in both Open Systems and Mainframe environments
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 32
SRDF Source and Target Volumes
SRDF R1 and R2 Volumes can have any local RAID Protection– E.g. Volumes could have RAID-1 or RAID-5 protection
SRDF R2 volumes are in a Read Only state when remote replication is in effect– Changes cannot be made to the R2 volumes
SRDF R2 volumes are accessed under certain circumstances– Failover – Invoked when the primary volumes become unavailable
– Split – Invoked when the R2 volumes need to be concurrently accessed for BC operations
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 33
Global Cache Director
DiskDirector (DD)
ChannelDirector (CD)
ChannelDirector (CD)
DiskDirector (DD)
Remote LinkDirector (RLD)
Remote LinkDirector (RLD)
Symmetrix Containing Target (R2) Volumes
Target Host
3
2
Global Cache Director
DiskDirector (DD)
ChannelDirector (CD)
ChannelDirector (CD)
DiskDirector (DD)
Remote LinkDirector (RLD)
Remote LinkDirector (RLD)
Symmetrix Containing Source (R1) Volumes
Source Host
1 4
1. Write received by Symmetrix containing Source volume
SRDF/Synchronous
Application does not receive I/O acknowledgement until data is received and acknowledged by remote Symmetrix
Write completion time is extended - No impact on Reads
Most often used in campus solutions
4. Write complete sent to host
3. Target Symmetrix sends acknowledgement to Source
2. Source Symmetrix sends write data to Target
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 34
SRDF Operations - Failover Purpose – Make Target Volumes Read Write
Source Volume status is changed to Read Only
SRDF Link is suspended
After
RWRO
Source Volume
TargetVolume
RORW
Source Volume
TargetVolume
Before
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 35
SRDF Operations - Failback
Makes target volume Read Only, resumes link, synchronize R2 to R1, and write enables source volume
RWRO
Source Volume
TargetVolume
Before
After
RORW
Source Volume
TargetVolume
sync
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 36
SRDF Operations - Split
Enables read and write operations on both source and target volumes
Suspends replication
RORW
Source Volume
TargetVolume
Before
After
RWRW
Source Volume
TargetVolume
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 37
SRDF Operations – Establish/Restore
Establish - Resume SRDF operation retaining data from source and overwriting any changed data on target
Restore - SRDF operation retaining data on target and overwriting any changed data on source
RORW
Source Volume
TargetVolume
Establish
RORW
Source Volume
TargetVolume
Restore
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 38
EMC CLARiiON MirrorView/A Overview
Optional storage system software for remote replication on EMC CLARiiON arrays– No host cycles used for data replication
Provides a remote image for disaster recovery– Remote image updated periodically - asynchronously
– Remote image cannot be accessed by hosts while replication is active
– Snapshot of mirrored data can be host-accessible at remote site
Mirror topology (connecting primary array to secondary arrays)– Direct connect and switched FC topology supported
– WAN connectivity supported using specialized hardware
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 39
MirrorView/A Terms
Primary storage system– Holds the local image for a given mirror
Secondary storage system– Holds the remote image for a given mirror
Bidirectional mirroring– A storage system can hold local and remote images
Mirror Synchronization– Process that copies data from local image to remote image
MirrorView Fractured state– Condition when a Secondary storage system is unreachable by the
Primary storage system
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 40
MirrorView/A Configuration
MirrorView/A Setup – MirrorView/A software must be loaded on both Primary and
Secondary storage system
– Remote LUN must be exactly the same size as local LUN
– Secondary LUN does not need to be the same RAID type as Primary
– Reserved LUN Pool space must be configured
Management via Navisphere Manager and CLI
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 41
ADC
MirrorView/A – Initial Synchronization
Host
Primary Image
Secondary Image
Snapshot
RLP
A B E FE’B’ B C D E F
E
Tracking DeltaMap
Transfer DeltaMap 1 1 1 1 1 10 0 0 0 0 0
00 00 0 01 1
MAP MAP
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 42
ADC
MirrorView/A – Update
Host
Primary Image
Secondary Image
Snapshot
RLP
A FE’B’ B C D E F
Tracking DeltaMap
Transfer DeltaMap
0 00 00 1 1Transfer DeltaMap
Tracking DeltaMap 0 0 0 0 0 0
MAP MAP
A’
1
0
B’
B
E”
E’
1
E
E’
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 43
ADC
MirrorView/A –Promotion (Update Failure)
Host
Primary Image
Secondary Image
Snapshot
RLP
F’E’B’ C D E F
00 00 1Transfer DeltaMap
Tracking DeltaMap 0 0 0 0 1
MAP MAP
A’
1
0
B’
B
E”
E’
1
B
Promote Secondary
Primary Image
© 2006 EMC Corporation. All rights reserved. Business Continuity – Remote Replication - 44
Consistency Groups
Group of secondary images treated as a unit
Local LUNs must all be on the same CLARiiON
Remote LUNs must all be on the same CLARiiON
Operations happen on all LUNs at the same time– Ensures a restartable image group