System Programmer Reference › Backing Up Data › Backing Up Non-CMS Minidisks › Change Detection for Physical Backups › Storing Change Detection Information for Physical Backups

Storing Change Detection Information for Physical Backups

When defining the full backup job template file, the CA VM:Backup system administrator can set one of the following for change detection during physical backups:

Hash

CA VM:Backup uses a hash value to determine whether the contents of a minidisk have changed.

If CA VM:Backup is creating file-level detail catalogs, CA VM:Backup computes a hash value of the contents of each CKD track or FBA group of blocks backed up and stores the values in the catalog.

If CA VM:Backup is creating domain-level catalogs, CA VM:Backup computes a hash value of the contents of each minidisk backed up and stores the values in the catalog.

Hash is the default option.

None

CA VM:Backup does not save hash values for change detection. When you select None, CA VM:Backup cannot detect changes; incremental backup jobs will perform a full backup of these minidisks.

The None option is the best choice when a minidisk:

• Changes frequently (an incremental backup will back up most of the minidisk anyway)
• Is restored frequently (a full backup minimizes the number of tape mounts required for the restore)

Not saving hash values reduces the number of CPU cycles CA VM:Backup uses and may result in improved backup performance.