Enhanced Remote Mirroring Utility; Description Of The Enhanced Remote Mirroring Utility; Operation Of The Enhanced Remote Mirroring Utility - IBM System Storage DS3000 Programming Manual

Enhanced Remote Mirroring utility

This section describes the host utility to achieve periodic consistency with Enhanced Remote Mirroring
configurations. This section also describes how to run the Enhanced Remote Mirroring utility.

Description of the Enhanced Remote Mirroring Utility

The Enhanced Remote Mirroring utility lets you 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 logical drive, or
collection of logical drives, at a secondary site ever reach a consistent, recoverable state.
The Enhanced Remote Mirroring utility enables you to bring a collection of 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 Enhanced Remote Mirroring 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 DS5000 Storage Manager 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 logical drives and mirrors.
Note: The Enhanced Remote Mirroring utility does not check to make sure that concurrently running
instances of the utility are not trying to process the same logical drives and mirrors. If you choose to
simultaneously run more than one instance of the Enhanced Remote Mirroring utility, you must make
sure that the configuration files that you choose to run do not list the same logical drives and mirrors.

Operation of the Enhanced Remote Mirroring Utility

The Enhanced Remote Mirroring utility performs steps that generate a recoverable state for multiple
mirror logical drives at a secondary site. The utility runs these steps to create consistent, recoverable
images of a set of logical drives:
1. On the primary storage subsystem – The utility reconfigures all of the participating logical drives
from Enhanced Global Mirror Group to Enhanced Remote Mirroring. This action makes sure that the
stream of write operations becomes recoverable on the secondary side.
On the primary storage subsystem – The utility polls all of the participating logical drives until the
2.
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 logical drives are cleared, and the
secondary logical drives are recoverable.
On the primary storage subsystem – The utility suspends the mirrored pairs for all of the
3.
participating logical drives. This action causes updates to stop on the secondary side, leaving the
secondary logical drives in a recoverable state because they were being updated in Synchronous mode
immediately before the suspension. By separating the mirrors in this manner, the primary-side
applications run faster, while leaving the secondary logical drives in a recoverable state. The delta log
tracks changes made because of application writes on the primary side while in this state.
Chapter 8. About Enhanced Remote Mirroring premium feature
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