Phase 3: Backing up migrated data sets

A migrated data set might not have a backup version because it has migrated after it was created or changed but before it was backed up. Such a condition could occur if a MIGRATE command were issued for the data set shortly after it was created or changed. The migration could be to either an ML1 volume or a DASD ML2 volume.

If DFSMShsm recalls the data set before it is backed up, DFSMShsm does not back up the data set from the migration volume. Instead, DFSMShsm backs up the data set when it backs up the DFSMShsm-managed volume that now contains the data set.

If you specify the BACKDS command to back up a migrated data set, DFSMShsm does not back up the data set again during this phase.

The primary host is the only host that backs up migrated data sets. Migrated data sets are backed up once a day and normally during automatic backup. However, if automatic backup is not scheduled to run on a particular day, you can use the BACKUP parameter of the RELEASE command to back up migrated data sets.

In backing up migrated data sets, DFSMShsm reads the required records in the BCDS. As each record is read, DFSMShsm passes control to the data set backup installation exit (ARCBDEXT) if the installation exit is enabled. If ARCBDEXT does not prevent backup, DFSMShsm checks (1) the BACKUP FREQUENCY attribute from the management class associated with the data set when the data set migrated, and (2) the recorded last backup date. If the number of days since the last backup date equals or exceeds the BACKUP FREQUENCY attribute value, DFSMShsm backs up the data set. If DFSMShsm cannot determine a last backup date and no backup version exists, it backs up the data set. If the number of days since the last backup date is less than the BACKUP FREQUENCY attribute value, DFSMShsm retains the information in the BCDS and does not back up the data set. If the exit returns a RETAINDAYS value for the data set, it is stored in the MCC and the MCB records.