Selecting daily backup volumes

When DFSMShsm selects a backup volume, it considers whether this is initial volume selection or subsequent volume selection.

If an error occurs during the selection process for a tape and the error is associated with a particular volume, DFSMShsm considers the tape backup volume unavailable for backup processing and selects another backup volume. Each time DFSMShsm is started, all nonfull backup volumes are considered available for backup processing.

The error handling and tape selection process differs when using the duplex tape option for your backup tapes.

Unless they are superseded by the BACKUPDEVICECATEGORY parameter of the BACKVOL or ADDVOL commands, the subparameters of the BACKUP parameter of the SETSYS command control the type of backup volume selected for output during backup processing:
  • SETSYS BACKUP(ANY) specifies that any type of backup volume (DASD) or TAPE) defined to DFSMShsm with the ADVOL command can be selected for output during backup processing. The backup volume has to be nonfull, unallocated, daily backup assigned to the current day in the backup cycle. You must ADDVOL DASD or TAPE volumes to DFSMShsm for volume selection. If none are defined or available, DFSMShsm fails the request.
  • SETSYS BACKUP(DASD) specifies that only DASD backup volumes are selected for output during backup processing.
  • SETSYS BACKUP(TAPE) specifies that only tape backup volumes are selected for output during backup processing. The automatic class selection (ACS) routines determine whether the backup function is directed to a system-managed tape library.
  • SETSYS BACKUP(TAPE(unittype)) specifies that only tape backup volumes are selected for output during backup processing. The ACS routines determine whether the backup function is directed to a system-managed tape library.

    When the backup function is not using a system-managed tape library, UNITTYPE specifies that only tape backup volumes capable of being mounted and written to on the specified type of unit are selected for output during backup processing.

DFSMShsm backs up users’ data sets to daily backup volumes during volume backup. Daily backup volumes either are assigned by the storage administrator to a day in the backup cycle before DFSMShsm uses them or are assigned when DFSMShsm selects a volume added as a backup volume.

During backup of a level 0 volume, backup of migrated data sets, or movement of backup versions, DFSMShsm searches for a target volume as follows:
  • It finds a volume already associated with the current day in the backup cycle that is neither full nor in use.
  • It reuses a previously full volume.
  • It assigns an additional volume.
  • It waits for another task to finish using an acceptable volume.

DFSMShsm stops the search as soon as it finds an acceptable volume. If it does not find an acceptable volume, DFSMShsm stops processing the requested backup function.

DFSMShsm determines which daily backup volume to use by considering:
  • The status of volumes previously used on this day in the backup cycle. This includes whether this is initial volume selection or subsequent volume selection.
  • The backup attributes of the volume being backed up.
  • The directions the storage administrator gives to DFSMShsm.

If an error occurs during the selection process and the error is associated with a particular volume, DFSMShsm considers the volume unavailable for backup processing and selects another daily backup volume. Each time DFSMShsm is started, the target volumes previously considered unavailable for backup processing are reinstated as available volumes.

When DFSMShsm initially selects a daily backup volume, it tries to find one that meets the following characteristics:
  • The volume is already assigned to the current day in the backup cycle.
  • The volume has the appropriate backup device category.
  • The volume is not full.
  • The volume is not being used by another task in this or another host.

After a volume backup task has obtained a daily backup volume, it continues to use that volume until the volume is no longer needed, the volume becomes full, or certain error conditions occur.

Now consider the processing that occurs when you specify the backup device categories of DASD, TAPE, or NONE.

Related reading

Parent topic: Automatic backup processing