Determining eligible data sets for backup

After DFSMShsm determines that a data set is eligible for a class transition or migration, it checks whether the data set needs to be backed up.

For class transitions, a data set must be backed up if the TRANSITION COPY TECHNIQUE specifies that fast replication should be used. If the data set has not been backed up and fast replication or preserve mirror are preferred, then standard data movement will be performed. If the data set has not been backed up and fast replication or preserve mirror are required, then the transition will fail.

A backup copy is required whenever fast replication is used because DFSMShsm processing for the data set completes before the data set is physically copied. While unlikely, it is possible for the physical copy to fail. Requiring a backup copy of the data set ensures the availability of the data set should the physical copy fail.

For migration, a data set must be backed up if all of the following criteria are met:

The data-set-changed indicator in the data set VTOC entry indicates that the data set has been changed.
The management class contains the attribute AUTO BACKUP=Y.
The management class ADMIN OR USER COMMAND BACKUP attribute contains either of the values ADMIN or BOTH.
The storage group has the attribute AUTO BACKUP=Y.

DFSMShsm identifies any migration-eligible data set that must be backed up. If the data set that must be backed up is identified for migration to tape, DFSMShsm removes the identification as a migration candidate.

If concurrent copy was used to backup the data set and a system failure or cancel of DFSMShsm occurred after the concurrent copy session was established, then the data-set-changed indicator can be off even though the data set was not successfully backed up. If this happens, migration will not identify the data set as needing a backup copy.