System Programmer Reference › Backing Up Data › Backing Up CMS Minidisks › Change Detection for CMS Backups › Detecting Changes During CMS Incremental Backups

Detecting Changes During CMS Incremental Backups

When defining the incremental backup job template file, the change detection options have the following meaning:

Date

CA VM:Backup compares the current FST attributes of a file to the corresponding attributes of the file stored in the base file-level detail catalog to determine whether the contents of the file have changed. If the base catalog contains domain-level detail, certain minidisk attributes are compared to the attributes in the base catalog. Date is the default option.

Hash

CA VM:Backup recomputes the hash value for each file along with its FST attributes and compares this value with the hash value stored in the base file-level detail catalog to determine whether the contents of the file have changed. If the base catalog contains domain-level detail, the minidisk contents are hashed and compared to the hash value stored in the base catalog.

When Date is used for a full backup, CA VM:Backup does not compute and store hash values for data. If Hash is defined for the incremental backup, CA VM:Backup cannot determine whether data has changed because there are no hash values in the catalog created by the full backup. When CA VM:Backup is unable to detect changes for a domain in an incremental backup, a full backup is taken of that domain.

When Hash is defined for the full backup, the hash value and FST information are stored in the catalog, which means CA VM:Backup can detect changes even when the file's FST attributes have not changed.

Notes:

• For information about setting these options in a backup job template file, see the OPTIONS record in the Template Programming Interface Guide.
• For information about managing change detection through administration screens, see "Specifying Change Detection" in the chapter "Managing Backup Job Template Files" in the Administration Guide.