Using Tape Storage Groups

You do not define tape volumes in tape storage groups as you do for DASD. Volumes are added to storage groups on use at open. Tape storage group definitions do not contain tape drives; they have privately owned tape volumes only. Multiple tape libraries can belong to a given tape storage group.

You can write the data class ACS routine to select the media interchange characteristics for the tape data set. If it is a tape mount management candidate, it can be assigned the TMMACTV, TMMBKUP, or TMMTEMP data class, and directed to the system-managed DASD buffer. If the data class ACS routine determines that the data set should be directly written to tape, based on the type of data written or the size of the data set, the data set is assigned the TAPOSITE, TAPTEMP, TAPACTV, or TAPBKUP data class. These data sets are written on system-managed volumes in the following way:

The storage class ACS routine must assign a storage class for the request to be SMS managed.
The storage group ACS routine assigns a tape storage group to the new tape allocation directly, and to a system-managed tape library and tape device pool indirectly.
When the storage group ACS routine selects a tape storage group:
- A list of tape device pools for the tape libraries belonging to the storage group is built.
  A device pool is a string of tape drives that is part of a system-managed tape library.
- The preferred tape device pools belong to tape libraries that are above their scratch volume threshold.
- This ordered list of tape device pools is used to select the tape drive.
  For a scratch volume, drives with active cartridge loaders containing the appropriate media type will be given preference. Tape management based scratch pools can be used with manual tape libraries and may restrict which volumes are allowed in response to the scratch request. DFSMSrmm pooling can be based on storage group assignments.
  
  Note that when you use DFSMShsm, you must use global scratch pools for storage group containing multiple automatic tape libraries. In this scenario, the tape device is selected first, followed by a tape. The tape and device must be in the same library, so using a private (HSM) scratch pool can result in running out of empty tapes for the tape device that was allocated while empty tapes exists for other tape libraries in the storage group.
- Once the data set is opened, the volume record in the tape configuration database is updated with the storage group assigned to the request. If you specify an expiration date, it is also stored in the volume entry. Lastly, recording technology, compaction, and media type are updated.
- If the user requests to catalog the data set, unlike SMS DASD, it is cataloged at disposition time, rather than allocation time.

Related Reading:

For specific RMM support, see z/OS DFSMSrmm Implementation and Customization Guide.
For information on the use of the Initial Access Response Time (IART) value in the Virtual Tape Server Environment, see z/OS DFSMS OAM Planning, Installation, and Storage Administration Guide for Tape Libraries.

For non-system-managed tape, you can use the SMS ACS routines to determine the scratch pooling on tape storage group names. See z/OS DFSMSrmm Implementation and Customization Guide for more information.