Implications of redefining the backup cycle

If you redefine the backup cycle, you might leave daily backup volumes unused.

Example: Assume the following conditions:

You have specified the DEFINE BACKUP(YNNYNNY) command. Automatic backup occurs on days 1, 4, and 7.
You have assigned volume A to day 1, volume B to day 4, and volume C to day 7.
You later specify DEFINE BACKUP(YNYN). Automatic backup occurs on days 1 and 3.

These are the results:

Volume A remains assigned to day 1.
Volume B is still assigned to day 4, but automatic backup no longer runs on day 4. Therefore, DFSMShsm does not use volume B unless someone issues a BACKVOL command on day 4 in the backup cycle.
DFSMShsm does not use volume C any more because it was assigned to day 7 and the new cycle has only four days.

To remove volume C (and volume B, if you want) from its day in the backup cycle and to make it an unassigned backup volume, use the DELVOL command. However, do not specify the PURGE parameter, because any backup version on the tape backup volume would be lost to DFSMShsm and the volume information for the tape or DASD volume would be deleted. The UNASSIGN parameter of the DELVOL command does not destroy any of the backup versions already contained on the volume or prevent DFSMShsm from accessing these backup versions during recovery, but it allows the volume to be used again if necessary.

In redefining the backup cycle, you can also use the CYCLESTARTDATE subparameter to redefine the starting date for the cycle.