If the data set has not changed and the backup version is created because the GUARANTEED BACKUP FREQUENCY has been met, then that backup version replaces the most recent backup version (replacement will not be performed for (H)BACKDS and BACKVOL TOTAL commands). If the data set has changed, backup versions are kept as described in the Specifying the maximum number of backup versions to keep topic that follows.
GUARANTEED BACKUP FREQUENCY (which is a maximum) takes precedence over the management class attribute BACKUP FREQUENCY (which is a minimum), such as in the following: If the BACKUP FREQUENCY is set to six days and GUARANTEED BACKUP FREQUENCY is set to four days, the data set is backed up after four days, whether the data set has been changed. If the attribute values are reversed, the data set is backed up after four days, if changed, or after six days if not changed.
GUARANTEED BACKUP FREQUENCY provides a way to reduce the number of tape mounts needed to recover a volume when a few data sets are not being changed. Volume dumps copy all data, even if nearly all of it is already backed up by incremental backup. Having all the data needed for a recovery on a small number of tapes can reduce the number of tape mounts needed to recover a volume entirely from incremental backups.
If the data set’s storage group attribute of AUTO BACKUP is NO, then no data sets are backed up by the automatic backup process, regardless of the setting of GUARANTEED BACKUP FREQUENCY. However, if an SMS volume is backed up by the BACKVOL command, GUARANTEED BACKUP FREQUENCY is honored for data sets that have not been changed.