Only incremental backups are possible within version backup: only modified files are saved, not modified files are skipped, it means no CNS entries are provided.
During the save run the file attribute NUM-OF-BACKUP-VERS is stored in the respective file record of the archive directory. From this value HSMS can decide how many file versions need to be kept in the archive or the other way round which old file versions can be removed during a reorganization run. (Reorganization is described in the next chapter).
However, in case not modified files have changed the number of backup version attribute or the value in the management class, to which the files are assigned, has been modified, the corresponding value in the version backup directory is updated correspondingly. This update is done during a save run for the files specified in the file names operand, but can be done also with the statement CHECK-CATALOGED-FILES.
For migrated files both the catalog entries and the data are always saved.
The backup class may be used as a criterion for deciding whether a file is to be backed up.