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Chapter 30. IIBM TotalStorage Rapid Data Recovery 465
Global Mirror
– Storage Server periodically forms Consistency Groups. Testing has shown that given
enough bandwidth, Storage Servers can form these groups on an average of every 3
to 5 seconds.
– When recovering to the recovery copy, software such as eRCMF examines the states
of the Global Mirror relationships and directs the Storage Server through the steps
necessary to recover that data to the last committed consistent copy.
It should be noted that eRCMF neither performs an automated recovery nor an automated
restart of systems in the remote site. Instead, eRCMF's freeze performs a controlled site
split
only. If a higher level of automation is required, eRCMF provides interfaces such as execution
scripts or a command line interface, which can be utilized and customized. When this occurs,
mirroring between Site 1 and Site 2 stops, ensuring the consistency of data. Further response
by the automation is determined by policies that are selected based on individual business
requirements:
Freeze and Go quickly executes the freeze to ensure data consistency, but then
immediately allows I/Os to continue. This allows processing to continue in the production
data center while maintaining a consistent copy of the data in either the backup or remote
data center. Meanwhile, the business is able to determine the cause of the event and
whether it is a disaster. If a disaster has not occurred, production has not been impacted
by an unnecessary site switch. If a disaster has occurred, then the data since the time of
the site split may need to be recreated if recovering to a backup or a remote data center.
Freeze and Stop quickly executes the freeze to ensure consistency but, rather than
immediately allowing the I/Os to continue, causes the ESS to block all further I/Os until
told otherwise. This ensures that no transactions, other than those in-flight at the time of
the event, need to be recreated following a disaster. If the event turns out not to be a
disaster, however, the production will be halted until the I/Os are freed.
30.4 Additional information
Further information can be found on the IBM Web site at:
http://www-1.ibm.com/services/us/index.wss/so/its/a1000110
For further information, you can refer to the following papers:
enterprise Remote Copy Management Facility eRCMF V4 Implementation Guide
enterprise Remote Copy Management Facility eRCMF V4 User Guide
You can find these papers at:
http://www-1.ibm.com/support/docview.wss?uid=ssg1S7001074
For more information, contact your IBM sales representative.