The Backstore Engine › USS Backstore › How the USS Backstore Works

How the USS Backstore Works

CA Vtape continues to use existing high speed mainframe DASD for Virtual Drive emulation in the IO Engine.

CA Vtape has added an optional USS Backstore copy attribute for Virtual Volumes that can be used in externalization policies defined by Group definitions through parmlib. This is in addition to the Primary and Duplex attributes. The USS Backstore copy is defined by the Triplex attribute.

Note: Triplex is mutually exclusive with the Export attribute meaning that if you define an Export attribute value you cannot define a Triplex value or vice versa.

Primary and Duplex copies Virtual Volumes to and from physical tape while Triplex copies them to and from USS files. The possible combinations of Backstore Copies are:

• Primary only
• Primary and Duplex
• Triplex only
• Primary and Triplex
• Primary, Duplex and Triplex

You can use the USS file system Triplex copy in addition to their traditional Primary and Duplex copies on physical tape. Or you can use the USS file system Triplex copy as a way to eliminate physical tapes. The USS file system can write to NFS servers which can be located in a cold DR site and can be a data de-duplication device that supports NFS. Any NFS server supported by z/OS can be used. CA Vtape does not provide replication or data de-duplication directly but can exploit these features if provided by the NFS server. Most data de-duplication NFS servers also offer data replication.

With the CA Vtape flexible policy based grouping, performance, replication, compression, and physical tape requirements can be assigned to suit the application.

During externalization, the group attributes determine how many tape drives are allocated and whether a Triplex file is to be created.

During recall, if USS Backstore is enabled, then any located Triplex copy is considered as an additional recall source. This is true whether the group currently has Triplex specified or not. The group attributes OffsiteBackstoreCopy and RecallAttemptsThreshold have been extended to consider the Triplex copy along with SET RECALL order operator command.

Note: For more information, see the section Automatic Recall Source Switching and the section Recall Sources in the Administration Guide.