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Document Sample
Business Continuity – Remote
Replication
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
Business Continuity – Remote
Replication -2
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– Remote which data is
Business Continuity
over
transported from source site to remote site
3 Replication -
Synchronous Replication
A write has to be secured on the
remote replica and the source before it
is acknowledged to the host Disk
Ensures that the source and remote 1
replica have identical data at all times
◦ Write ordering is maintained at all times 4
Server
Replica receives writes in exactly the same
order as the source
Data Write 3 2
Data Acknowledgement
Synchronous replication provides the
lowest RPO and RTO
◦ Goal is zero RPO
Disk
◦ RTO is as small as the time it takes to
start application on the remote site
Business Continuity – Remote
Replication -4
Synchronous Replication
Response Time Extension
◦ Application response time will be
extended due to synchronous
replication Max
Data must be transmitted to remote
site before write can be Writes
acknowledged MB/s
Time to transmit will depend on
distance and bandwidth
Bandwidth Average
◦ To minimize impact on response time,
Time
sufficient bandwidth must be provided
for at all times
Rarely deployed beyond 200 km
Business Continuity – Remote
Replication -5
Asynchronous Replication
Write is acknowledged to
host as soon as it is
received by the source Disk
1
Data is buffered and sent
to remote Server
2
◦ Some vendors maintain write ordering Data Write 4 3
◦ Other vendors do not maintain write Data Acknowledgement
ordering, but ensure that the replica will
always be a consistent re-startable image
Finite RPO Disk
◦ Replica will be behind the
Source by a finite amount
◦ Typically configurable Continuity – Remote
Business
Replication -6
Asynchronous Replication
Response Time unaffected
Bandwidth
◦ Need sufficient bandwidth on average Max
Buffers
◦ Need sufficient buffers Writes
MB/s
Can be deployed over long distances
Average
Time
Business Continuity – Remote
Replication -7
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
Business Continuity – Remote
Replication -8
LVM Based Remote Replication
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
Log Log
Physical Physical Physical Physical Physical Physical
Volume 1 Volume 2 Volume 3 Volume 1 Volume 2 Volume 3
Network
Volume Group Volume Group
Local Site Remote Site
Business Continuity – Remote Replication -9
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
Business Continuity – Remote
Replication - 10
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
Business Continuity – Remote
Replication - 11
Host Based Log Shipping
Logs
IP Network
Original
Offered by most DB Vendors
Advantages
◦ Minimal CPU overhead
◦ Low bandwidth
◦ Standby Database consistent Logs
to last applied log
Stand By
Business Continuity – Remote
Replication - 12
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 operations
Production Array Remote Array
Network
Production Source Replica
Server
Distance DR Server
Business Continuity – Remote
Replication - 13
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 remote array
Remote array sends acknowledgement to the source
array
Source array signals write complete to host/server
Business Continuity – Remote
Replication - 14
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 remote array
Remote array sends acknowledgement to the source
array
No impact on response time
Extended distances between arrays
Lower bandwidth as compared to Synchronous
Business Continuity – Remote
Replication - 15
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
Business Continuity – Remote
Replication - 16
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
Business Continuity – Remote
Replication - 17
Extended Distance Consistent PIT
SOURCE REMOTE
Network Links
Source Local
Replica
Local Remote
Replica Replica
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
Business Continuity – Remote
Replication - 18
Synchronous + Extended Distance
Consistent PIT
SOURCE BUNKER REMOTE
Sync Network Local
Remote
Source Links Replica
Replica
Local Remote
Replica Replica
Network
Links
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
Business Continuity – Remote
Replication - 19
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
Business Continuity – Remote
Replication - 20
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
Business Continuity – Remote
Replication - 21
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
Business Continuity – Remote
Replication - 22
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
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
Business Continuity – Remote
Replication - 23
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.
Optical Channels
ESCON
Optical
Fibre Channel Optical Electrical
Lambda λ
Gigabit Ethernet
Business Continuity – Remote
Replication - 24
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
Business Continuity – Remote
Replication
25
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?
Business Continuity – Remote
Replication - 26
