Backup and recovery functions

The backup function is a data-set-level function when DFSMShsm is processing SMS-managed volumes. That is, the management class attributes define how the data set is treated for creation and retention of backup versions. Thus, on the same volume you can have data sets with different:

Permissions for automatic backup
Conditions for command backup
Minimum frequencies of backup
Numbers of backup versions
Retention periods for backup versions

For backup, DFSMShsm makes copies (versions) of changed data sets residing on level 0 volumes onto backup volumes. DFSMShsm uses the management class attributes and the guaranteed backup frequency attribute of the storage group for each data set to determine whether to copy the data set. After the data sets have been backed up, DFSMShsm determines from the management class attributes for each data set how many backup versions to keep and how long to keep them.

Backup can occur to either DASD or tape, whichever you specify. If backup is performed to DASD, your DASD volumes can become filled with the current backup versions and earlier backup versions that have not been discarded. When DASD backup volumes become full, DFSMShsm transfers the old (non-current but valid) backup versions to spill backup volumes. Transfer of valid versions from DASD backup volumes can be either to tape or to DASD.

If the backup or the spill processes are performed to tape, the tapes eventually contain many not valid versions that have been superseded by the more current versions that have been made. When tape volumes have many not valid versions, they are selected by the recycle process, which moves valid versions to spill backup volumes.

Recovery, the reverse of backup, returns data sets from the daily backup volumes or the spill backup volumes to the level 0 volumes. Recovery can be performed only by command, for individual data sets or for complete volumes.