Automatic backup deregistration considerations

The first step when recovering a VSAM sphere from a corruption is restoring the sphere from a backup.

Therefore, thoughtful planning is required prior to specifying an automatic backup retention period through the CICS® VR panel interface. A few items to consider during this planning are:

Backup creation interval
Do not specify a backup retention period that is smaller than your backup creation interval. This could result in unrecoverable updates. For example, consider the following scenario:
  • Backups are taken for all spheres every eight days
  • Log data is retained for eight days
  • Backups are retained for six days

In the above scenario, a backup might be deleted before a new one for the same VSAM data set is created. Therefore, if the data set become corrupted, it might not be recoverable because a backup does not exist. Even though log data exists since the last backup was taken, recovery must always begin with restoring the data set from a backup.

If you specify an automatic backup retention period through the CICS VR panel interface, IBM® recommends that:
  • If all your data sets are backed up during the same interval, at a minimum, the specified backup retention period is one day greater than the backup interval.
  • If your data sets are backed up with varying intervals, at a minimum, the specified backup retention period is one day greater than the largest backup interval.
Note: The specified CICS VR automatic backup deregistration criteria applies to all registered backups for all registered VSAM spheres. Also, it might be desirable to keep multiple backups for each VSAM sphere if you have a problem restoring one of the backups, as long as corresponding log data still exists for the backups.
Log data relation

For recovery purposes, backups are only valuable if log records that were written for updates made to the data set immediately after the backup was created, up to the time of corruption, still exist, either on the forward recovery log stream, change accumulation data set, or log stream copy. Therefore, when log data is deleted from the log stream, change accumulation data set, and log stream copy, backups that were created prior to the deleted log data can also be deregistered and deleted.

If you have specified an automatic log stream deregistration retention period, you can also specify 'Use log retention period' as the automatic backup deregistration retention criteria. This causes CICS VR automatic deregistration processing to deregister, and optionally uncatalog and delete, any backups that are older than the automatically deregistered log data.

Individual backup retention periods

Any specified CICS VR automatic backup deregistration setting applies to all registered backups for all registered VSAM spheres. You might therefore consider using other software to manage the deletion of your backups, when your environment requires you to specify individual or different retention criteria for your backups. However, if your backups are being deleted outside of CICS VR by another product, they must also be deregistered from the CICS VR RCDS, to avoid the RCDS becoming full and outdated information being displayed through the CICS VR panel interface. You can dynamically deregister backups individually through the CICS VR panel interface. However, you can also specify Use catalog information as the automatic backup deregistration criteria. This causes CICS VR automatic deregistration processing to query the ICF catalog for all registered backups. All backups for which the ICF catalog does not return an entry is automatically deregistered from the RCDS.

The Use catalog information automatic backup deregistration criteria can also be useful in disaster recovery scenarios. For example, you might have sent several items, including log copies, backups, and a copy of the RCDS to your remote recovery site. However, you might have only sent a subset of all registered backups to your remote site. Therefore, prior to building the recovery job, at your remote recovery site you might want to specify the Use catalog information automatic backup deregistration criteria, then run automatic deregistration. This results in the CICS VR panel interface only displaying the registered backups that have been sent and cataloged at the remote recovery site.


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Timestamp icon Last updated: Friday, 7 February 2014


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