Snapshot backup of individual mirrors

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IBM® Storage Protect Snapshot supports mirroring.

Mirroring by using the AIX® logical volume manager (LVM mirroring)

IBM Storage Protect Snapshot provides LVM mirroring support for the following storage devices:
  • DS8000®
  • IBM XIV® Storage System
  • Storwize® family
  • SAN Volume Controller

For those devices, IBM Storage Protect Snapshot creates a snapshot backup where only one of the mirrors is copied during the backup. When LVM is used to mirror the database across sites, you can create offloaded tape backups on either site with IBM Storage Protect Snapshot. In this situation, you do not have to transfer the backup image across sites. To complete this task, a backup server is required on either site where backup images can be mounted to transfer them to secondary backup media.

For DS8000, you can create at most one INCREMENTAL snapshot per source volume. However, in LVM environments, each source volume is mirrored. Therefore, IBM Storage Protect Snapshot can create two INCREMENTAL snapshot backups for DS8000.

Figure 1. Cross-site mirrored SAP database that is protected with IBM Storage Protect Snapshot and an IBM Storage Protect server.

Cross-site mirrored SAP database that is protected with IBM Storage Protect Snapshot and IBM Storage Protect)

AIX LVM mirroring advantages

  • Only one of the two LVM mirrors are used for the snapshot. Using one mirror saves the number of needed target volumes and reduces the time that is needed for creating the snapshot.
  • Avoids unnecessary performance degradation within the storage system.
  • All LVM mirrors on the production system remain synchronized when the snapshot is created.
  • Online or offline snapshot backups can be created in both LVM mirrored and non-LVM mirrored environments. The backup and restore procedures as provided in the applicable documentation remain unchanged.
  • The snapshot backup process at no time compromises the high-availability purpose for which the mirrors were set up. It is not necessary to resynchronize the logical volumes after the snapshot backup request.
  • IBM Storage Protect Snapshot provides information about asymmetrical LVM mirror setups when they are encountered. The snapshot backup can fail in such environments, indicating a general deficiency of the high-availability setup.

IBM Storage Protect Snapshot requires that the LVM mirroring sets are in different storage subsystems. For example, different SAN Volume Controller clusters. Complete mirrors must be stored on both storage clusters. If this setting is not possible, IBM Storage Protect Snapshot continues processing for those clusters where a complete image of the application can be found.

To configure IBM Storage Protect Snapshot for LVM mirroring, define both storage subsystems within the IBM Storage Protect Snapshot profile. Use the DEVICE_CLASS parameter to allow IBM Storage Protect Snapshot to select the storage subsystem. At least one backup server is required so that IBM Storage Protect Snapshot can mount a snapshot backup to verify the consistency of the backup and split the LVM mirrors.

During a restore operation, IBM Storage Protect Snapshot runs all the commands that are required to prepare the LVM environment again for the second mirror. The administrator is informed by message FMM0755I in the detailed restore log file that the volume groups are ready for synchronization. The administrator can run this operation at a more suitable time for instance after completion of the database recovery.
Note: The administrator must examine the log files for these messages. They do not display on the screen.

Support of AIX enhanced concurrent capable volume groups

To support high-availability environments, IBM Storage Protect Snapshot supports enhanced concurrent capable volume groups.

Heterogeneous device mirroring

IBM Storage Protect Snapshot does not require the storage devices of different mirrors to be at the same version level.