Appendix C. Global Copy Mirror Utility - IBM System Storage DS3000 Programming Manual

Appendix C. Global Copy mirror utility

This appendix describes the host utility to achieve periodic consistency with Global Copy Mirror
configurations. This appendix also describes how to run the Global Copy utility.
Note: The Global Copy Mirror utility works only with the synchronous remote mirror commands. This
utility does not work with the Enhanced Global Remote Mirror commands.
Description of the Global Copy Mirror Utility
The Global Copy Mirror utility enables you to periodically synchronize the Enhanced Remote Mirroring
pairs in your storage subsystem. When defining a Enhanced Remote Mirroring configuration, you have
the option to set the write modes to either Synchronous or Asynchronous. Metro Mirror provides the
highest level security for full data recovery from the secondary storage subsystem in the event of a
disaster. Metro Mirror does, however, reduce host I/O performance. Global Copy offers faster host I/O
performance, but it does not guarantee that a copy operation has successfully completed before
processing the next write request. With Global Copy, you cannot make sure that a volume, or collection
of volumes, at a secondary site ever reach a consistent, recoverable state.
The Global Copy Mirror utility enables you to bring a collection of Enhanced Global remote logical drives
into a mutually consistent and recoverable state. You can choose to run the utility based on application
demands, link state and speed, and other factors that are relevant to your environment.
The Global Copy Mirror utility has these characteristics:
v The utility is implemented as a command line-invoked Java-based application.
v The utility is bundled as part of the IBM DS Storage Manager 10 installation package.
v The utility accepts a command line argument that lets you specify the name of a configuration file that
contains a complete specification of the work to be carried out by the utility.
v More than one instance of the utility can run concurrently, as long as the utilities do not try to process
any of the same volumes and mirrors.
Note: The Global Copy Mirror utility does not check to make sure that concurrently running instances of
the utility are not trying to process the same volumes and mirrors. If you choose to simultaneously run
more than one instance of the Global Copy Mirror utility, you must make sure that the configuration files
that you choose to run do not list the same volumes and mirrors.
Operation of the Enhanced Remote Mirroring utility
The Global Copy Mirror utility performs steps that generate a recoverable state for multiple mirror
volumes at a secondary site. The utility runs these steps to create consistent, recoverable images of a set
of volumes:
1. On the primary storage subsystem – The utility reconfigures all of the participating volumes from
Global Copy mirroring to Metro Mirror mirroring. This action makes sure that the stream of write
operations becomes recoverable on the secondary side.
2. On the primary storage subsystem – The utility polls all of the participating volumes until the
associated mirror states all have the Optimal state. In cases where the remote link is slow or the
primary host I/O activity is high, one or more mirrors are likely to be in the Unsynchronized state
before they migrate to the Synchronized state. By waiting until all of the mirrors have Optimal status,
the utility makes sure that all of the delta logs for the affected volumes are cleared, and the secondary
volumes are recoverable.
© Copyright IBM Corp. 2008, 2012
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