Specifying how long to keep backup versions

You can control how long to keep extra backup versions for data sets, how long to keep the only backup version of data sets that have been deleted, and how long to keep specific backup versions. (DFSMShsm does not delete the only backup version of a data set that exists unless you specifically delete the backup version.) The attributes that control the number of days to keep extra backup versions are overridden by the attributes that control the number of versions to keep. That is, if you have more backup versions than are specified by the appropriate NUMBER OF BACKUP VERSIONS attribute, the excess versions are deleted by the EXPIREBV command even though they may not have reached the age specified by the RETAIN DAYS attributes. The retention period for a specific backup version can be specified with the RETAINDAYS keyword on the data set backup command. The value specified on the RETAINDAYS keyword overrides all other retention values.

The RETAIN DAYS EXTRA BACKUP VERSIONS attribute controls the number of days that you keep backup versions that are older than the most recent one. You can specify values from 1 to 9999 or NOLIMIT for this attribute. If you use the NOLIMIT value, you can delete extra backup versions based on the following criteria:

The value you assign to the NUMBER OF BACKUP VERSIONS attribute.
The issuance of a DFSMShsm command to delete specific backup versions.
The value assigned to the RETAIN DAYS ONLY BACKUP VERSION attribute.
Note: All remaining backup versions are deleted after the retention period specified if you assign a value other than NOLIMIT.

The RETAIN DAYS ONLY BACKUP VERSION (DATA SET DELETED) attribute controls how long the last backup version is retained after the data set has been deleted. You can specify values from 1 to 9999 or NOLIMIT. If you use the NOLIMIT value, the last remaining backup version can be deleted only by the value of the NUMBER OF BACKUP VERSIONS attribute being zero, or by a DFSMShsm command to delete the specific backup version. The default for RETAIN DAYS ONLY BACKUP VERSION (DATA SET DELETED) is 60. The number of days is counted from the time that DFSMShsm detects that the data set has been deleted. DFSMShsm detects that the data set has been deleted when the EXPIREBV command is processed.

When RETAIN DAYS ONLY BACKUP VERSION is set to other than NOLIMIT (1 to 9999), and the RETAIN DAYS EXTRA BACKUP VERSION is set to NOLIMIT, the resulting effect is to keep the number of backup versions specified by the NUMBER OF BACKUP VERSIONS (DATA SET DELETE) attribute for the amount of time specified by the RETAIN DAYS ONLY BACKUP VERSION attribute. After the retention period, all remaining backup versions are deleted. If NOLIMIT is specified for both RETAIN DAYS EXTRA BACKUP VERSION and RETAIN DAYS ONLY BACKUP VERSION, the backup versions are not deleted by EXPIREBV.