Data set retirement

For those primary volumes with the DELETEIFBACKEDUP space management technique, DFSMShsm checks the backup control data set (BCDS) to be sure that a current backup version of the data set exists before DFSMShsm scratches the data set based on its inactive age. You specify the inactive age when you specify the space management technique. DFSMShsm scratches a data set even if the expiration date has not been reached.

DFSMShsm creates backup versions when automatic or command backup runs. If a backup version is made on the date the data set is last opened, DFSMShsm does not consider the backup version to be current. This means that DFSMShsm must make a backup version of a cataloged data set on the calendar day after the last activity of the data set. For non-VSAM data sets, the backup must be made after the last-referenced day. For VSAM data sets, the backup must be made after the last-update day. Therefore, if you want to use data set retirement often, schedule backup to run soon after midnight.

By running backup soon after midnight, you reduce your exposure to having the last backup made on the same date that the data set was last changed. If the data set is changed before midnight, automatic backup only occurs on the next calendar date, so the dates would not be the same. There are two possible scenarios where exposures might occur:

Data sets that were changed and then backed up by command on the same day
Data sets that were changed between midnight and the time that automatic backup encountered them in the course of its processing

Table 1 shows what DFSMShsm considers to be the current backup version of migrated and unmigrated data sets.

Table 1. Current Backup Version of Data Sets
Type of Data Set	Current Backup Version
Not migrated VSAM	DFSMShsm made the backup version since the last day someone updated the data set.
Not migrated, cataloged, non-VSAM	The update flag is off and the date-last-referenced that existed when the data set was backed up is earlier than the date the data set was last backed up.
Uncataloged, non-VSAM	The update flag is off and DFSMShsm made a backup version of the data set from the volume being processed.
Migrated VSAM	The update flag is off and DFSMShsm created the backup version after the date DFSMShsm last migrated the data set.
Migrated non-VSAM	The update flag is off and the date-last-referenced that existed when the data set was migrated is earlier than the date the data set was last backed up.

During data set retirement, DFSMShsm marks the latest backup version as a retirement version and gives it special protection against inadvertent deletion.

As DFSMShsm examines each data set for retirement, it passes control to the data set deletion installation exit (ARCADEXT).