Remote mirroring and consistency groups

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You must verify the configuration of the consistency group on SAN Volume Controller and XIV® systems that use mirroring functions before you run IBM® Storage Protect Snapshot backup operations.

A consistency group is a group of copy relationships. You can group relationships into a consistency group that manages the consistency of dependent writes by creating a consistent point-in-time copy across multiple volumes or storage systems.

You must ensure that the connectivity state is online and configured for a SAN connection between the primary and secondary storage systems. The primary site contains the primary storage volumes for the production site. The volumes are then replicated to target volumes on the secondary site. IBM Storage Protect Snapshot requires the following configuration:
  • For SAN Volume Controller, you must configure the consistency group:
    • For Metro Mirrors for static and dynamic target allocation, ensure that the state of the consistency group is consistently synchronized.
    • For Global Mirrors with dynamic target allocation, you must configure a Global Mirror with Change Volumes relationship:
      • Ensure that the consistency group for the relationship has cycling mode set to multiple by selecting the Global Mirror with Change Volumes option when you create the relationship between the volumes. Global Mirror with Change Volumes is the name for a point-in-time asynchronous volume replication. You can create change volumes either when you create the Global Mirror relationships or you can add them to an existing relationship. Cycling mode and change volumes are not needed when you assign target allocation manually.

      • The cycle period time set for the cycling mode and the number of I/O operations can influence the IBM Storage Protect Snapshot FlashCopy® backup time. IBM Storage Protect Snapshot waits until the volumes at both sites are synchronized before a backup operation is completed. The cycle period is defined in seconds. The higher the cycle period the longer the time that is required for synchronization and to complete a FlashCopy backup. The factors that can influence the time are the number of I/O operations and the spread of the block-level changes across the storage system. The default value is 300 seconds.

        Restriction: When you set the cycle period, the initial replication from the primary site change volume to the secondary change volume can take several hours before the volumes are synchronized. If you start an IBM Storage Protect Snapshot backup operation during this initial replication, the backup operation can fail due to the amount of time that is taken to complete the synchronization operation. Therefore, wait until the initial replication of change volumes is completed before you start a backup operation.
  • For XIV systems, you must configure the consistency groups:
    • The consistency group must contain a list of mirrors.
    • The consistency group must contain a list of all of the remote copy target-volumes and this list must exist before you start the snapshot on the remote system.
    • The mirror relationship between the master (source) and slave (target) volumes must be defined in the consistency group. The master is on the source volume. The slave is on the target volume.
    • For synchronous mirroring, the state of the consistency group must be consistently synchronized.
    • For asynchronous mirroring, the state of the consistency group must be RPO_OK.