In a backup to magnetic tape cartridge, the save file is automatically duplicated if the following requirements are met:
A shadow archive was assigned to the backup archive concerned.
Automatic duplication has not been deactivated. In other words: in the OPERATION-CONTROL operand of the HSMS statement BACKUP-FILES, the value *ALLOWED must be specified for SHADOW-COPY.
The save file is copied into the assigned shadow archive at the end of the backup run. The copy in the shadow archive is given the same save version ID and save file ID as the original, i.e. it receives the same time stamp.
If the directory file is to be saved at the end of the backup run (SAVE-DIRECTORY=*YES), the directory file of the assigned shadow archive is also saved at the end of the automatic duplication.
The directory file of the shadow archive, however, can differ from that of the associated backup archive because not all backups are copied to the shadow archive (backups to disk, backups for which SHADOW-COPY=*INHIBITED is specified, a new shadow archive can be linked to a non-empty backup archive).
If a save file in a backup archive is to be extended, the automatic duplication mechanism also attempts to extend the save file with the same SFID in the associated shadow archive. If this save file does not exist, duplication (and possible deletion of the files) is not carried out.
When copying explicitly to the shadow archive a new save file is generated there or an existing save file is updated in the same way as when saving in the main archive.
In the context of a disaster prevention strategy it may make sense to store the tape copy immediately in a specially protected room after every copy operation. However, the save files in the shadow archive cannot then be updated as in the main archive, but a new save file must be created after each copy operation. This mode is set using the archive attribute SHADOW-COPY=*ALLOWED-AND-NEW-SFID.
The automatic duplication mechanism enables the precautionary measures against data loss to be adapted to the requirements and to the storage capacity of a computer center:
Maximum data security, with very high costs with regard to tape consumption and high costs with regard to backup times:
Each system backup archive is assigned a shadow archive.
All backups are performed with the specification SHADOW-COPY=*ALLOWED and the archive attribute SHADOW-COPY=*ALLOWED-AND-NEW-SFID.
Result:
Every backup on S2 is automatically copied to the shadow archive and the tape copy is then immediately placed in a secure storage location.
Maximum data security, with high costs with regard to tape consumption and backup times:
Each system backup archive is assigned a shadow archive.
All backups are performed with the specification SHADOW-COPY=*ALLOWED.
Result:
Every backup on S2 is automatically copied into the shadow archive.
Medium data security, with average costs for tape consumption and backup times:
Each system backup archive is assigned a shadow archive.
All weekly full backups are performed with the specification SHADOW-COPY= *ALLOWED.
The incremental backups in between are performed with the specification SHADOW-COPY=*INHIBITED.
Result:
Only the weekly full backups on S2 are copied to the shadow archive.
Low data security, with lower costs for tape consumption and backup times:
No shadow archives are assigned to the system backup archives.
Result:
The automatic duplication mechanism is not used.