Transcript Remote Replication

Remote Replication
Module 3.4
© 2009 EMC Corporation. All rights reserved.
Remote Replication
After completing this module, you will be able to:
 Explain remote replication technologies
– Synchronous and asynchronous
 Discuss host and array based remote replication
– Functionality
– Differences
– Selecting the appropriate technology
 Discuss network options for remote replication
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What is Remote Replication?
 Replica is created at remote site
– Addresses risk associated with regionally driven outages
– Could be a few miles away or half way around the globe
 Modes of remote replication (based on RPO requirement)
– Synchronous Replication
– Asynchronous Replication
Source site
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Remote site
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Synchronous Replication
 A write must be committed to the
source and remote replica before it is
acknowledged to the host
Source
 Ensures source and remote replica
have identical data at all times
1
4
– Write ordering is maintained
 Replica receives writes in exactly the
same order as the source
 Synchronous replication provides the
lowest RPO and RTO
– Goal is zero RPO
Host
2
3
Data Write
Data Acknowledgement
Target
– RTO is as small as the time it takes to
start application on the target site
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Synchronous Replication: Bandwidth Requirement
 Response Time Extension
– Application response time will be
extended
 Data must be transmitted to target site
before write can be acknowledged
 Time to transmit will depend on
distance and bandwidth
Required bandwidth
Max
Typical workload
Writes
MB/s
 Bandwidth
– To minimize impact on response time,
sufficient bandwidth must be provided
at all times
Time
 Rarely deployed beyond 200 km
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Asynchronous Replication
 Write is committed to the source and
immediately acknowledged to the
host
Source
1
 Data is buffered at the source and
transmitted to the remote site later
2
– 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
Host
4
3
Data Write
Data Acknowledgement
 Finite RPO
Target
– Replica will be behind the source by a finite
amount
– Typically configurable
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Asynchronous Replication: Bandwidth Requirement
 Response time unaffected
Typical
workload
 Bandwidth
Required
bandwidth
– Need average bandwidth
 Buffers
– Need sufficient buffers
Writes
MB/s
Average
 Can be deployed over long distances
Time
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Remote Replication Technologies
 Host based
– Logical Volume Manager (LVM) based
 Support both synchronous and asynchronous mode
– Log Shipping
 Storage Array based
– Support both synchronous and asynchronous mode
– Disk Buffered - Consistent PITs
 Combination of Local and Remote Replication
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LVM Based
 Duplicate Volume Groups at source
and target sites
– All writes to the source Volume Group
are replicated to the target Volume
Group by the LVM
– Can be synchronous or asynchronous
mode
 In the event of a network failure
IP
– Writes are queued in the log file and
sent to target when the issue is resolved
– Size of the log file determines length of
outage that can be withstood
 Upon failure at source site, production
can be transferred to target site
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LVM Based – Advantages and Limitation
 Advantages
– Different storage arrays and RAID protection can be used at the
source and target sites
– Response time issue can be eliminated with asynchronous mode,
with extended RPO
 Limitations
– Extended network outages require large log files
– CPU overhead on host
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Host Based Log Shipping
Logs
IP
Original
 Offered by most database
Vendors
 Advantages
– Minimal CPU overhead
– Low bandwidth requirement
– Standby Database consistent
to last applied log
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Logs
Stand By
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Storage 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 business operations
Source Array
Target Array
IP/FC
Network
Source
Production
Server
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Distance
Replica
DR Server
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Array Based – Synchronous Replication
Network links
Source
Target
Write is received by the source array from host/server
Write is transmitted by source array to the target array
Target array sends acknowledgement to the source array
Source array signals write complete to host/server
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Array Based – Asynchronous Replication
Network links
Source
Target
Write is received by the source array from host/server
Source array signals write complete to host/server
Write is transmitted by source array to the target array
Target array sends acknowledgement to the source array
 No impact on response time
 Extended distances between arrays
 Lower bandwidth as compared to Synchronous
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Asynchronous Replication: Ensuring Consistency
 Maintain write ordering
– Some vendors attach a time stamp and sequence number with each
write, then send the writes to remote array
– Apply these writes to the remote devices in exact order based on the
time stamp and sequence numbers
 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 current buffer is closed in a consistent manner
and the buffer is switched, new writes are received in the new buffer
– Closed buffer is then transmitted to the remote array
– Remote replica will contain a consistent, re-startable image on the
application
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Array Based – Disk Buffered Replication
 Local and Remote replication technologies can be
combined to create consistent PIT copies of data on
target arrays
 RPO usually in the order of hours
 Lower Bandwidth requirements
 Extended distance solution
Source Data
Source
Host
Local Replica
Source Storage Array
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Local Replica
Remote Replica
Target Storage Array
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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 business 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 resynchronization between the source and replica
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Array Based – Which Technology?
 Synchronous
– Is a must if zero RPO is required
– Need sufficient bandwidth at all times
– 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 capacity
 Disk buffered
– Extended distance solution with RPO in the order of hours
– Require lower bandwidth than synchronous or asynchronous
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Three Site Replication
 Eliminates disadvantages of two site replication
– Single site disaster leads to a window when there is no DR
protection
 Data replicated to two remote sites
 Implemented in two ways
– Three Site Cascade/Multi-hop
– Three Site Triangle/Multi-target
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Three Site Replication – Cascade/Multi-hop
 Synchronous + Disk Buffered
Source Data
Remote Replica
Local Replica
Synchronous
Disk Buffered
Remote Replica
Local Replica
Bunker Site
Source Site
 Synchronous + Asynchronous
Source Data
Remote Site
Remote Replica
Synchronous
Local Replica
Asynchronous
Remote Replica
Local Replica
Source Site
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Bunker Site
Remote Site
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Three Site Replication – Triangle/Multi-target
BUNKER
Asynch
with
Differential
Resynch
SOURCE
REMOTE
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SAN Based Remote Replication
 Replicate from one storage array
to any other storage array over
the SAN/WAN
EMC Symmetrix
EMC CLARiiON
– Implement tiered storage
– Data migration
– Remote vaulting
SAN/WAN
 Heterogeneous arrays support
Hitachi
 Application and OS independent
 No impact to servers or the LAN
HP
IBM
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SAN Based Replication : Terminologies
 Control Array: Array responsible for the replication operations
– Control Device: Device on controlling array to/from which data is being
replicated
 Remote Array: Array to/from which data is being replicated
– Remote Device: Device on remote array to/from which data is being
replicated
 Operation
– Push: Data is pushed from control array to remote array
– Pull: Data is pulled to the control array from remote array
Remote Array
Control Array
C
Control Device
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SAN/WAN
PUSH
PULL
C
Remote Device
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Network Options for Remote Replication
 A dedicated or a shared network must be in place for
remote replication
– Use ESCON or FC for shorter distance
– For extended distances, an optical or IP network must be used
– Example of optical network: DWDM and SONET
 Protocol converters may require to connect ESCON or FC adapters from
the arrays to these networks
– Native GigE adapters allows array to be connected directly to IP
Networks
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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
 Up to 32 protected and 64 unprotected separate
wavelengths of data can be multiplexed into a light
stream transmitted on a single optical fiber
Optical Channels
ESCON
Fibre Channel
Optical
Electrical
Optical
Lambda λ
Gigabit Ethernet
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Synchronous Optical Network (SONET)
 SONET is Time Division Multiplexing
(TDM) technology
OC48
OC3
 Traffic from multiple subscribers is
multiplexed together and sent out onto
SONET ring as an optical signal
SONET
 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
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STM-16
STM-1
SDH
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Module Summary
Key points covered in this module:
 Modes of remote replication
– Synchronous and asynchronous mode
 Host based remote replication
– LVM based and log shipping
 Array based remote replication
– Synchronous, asynchronous and disk buffered
– Three site replication
– SAN based remote replication
 Network options for remote replication
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Concept in Practice – EMC Remote Replication
 EMC Symmetrix Arrays
– EMC SRDF/Synchronous
– EMC SRDF/Asynchronous
– EMC SRDF/Automated Replication
 EMC CLARiiON Arrays
– EMC MirrorView/Synchronous
– EMC MirrorView/Asynchronous
 EMC SAN Copy
– SAN based remote replication solution for EMC CLARiiON
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 Check Your Knowledge
 What is the difference between Synchronous and
Asynchronous mode?
 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?
 Discuss the effects of a bunker failure in a three-site
replication for the following implementation:
− Multihop—synchronous + disk buffered
− Multihop—synchronous + asynchronous
− Multitarget
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