Storage groups and automated class selections routines

A tape storage group is a collection of tape cartridges that are located within one or more tape libraries. Only a tape storage group may be used in association with tape libraries. As part of the definition of a tape storage group, one to eight library names can be associated with the tape storage group. Tape storage groups can have on each system or system group in the SMS complex any one of the following four attributes:

ENABLED: The system can create and access data sets on any tape volume belonging to this storage group. This condition can be changed by the VARY SMS,STORGRP operator command.
NOTCON: The system cannot create or access data sets on any tape volume belonging to this storage group. This condition cannot be changed by the VARY SMS,STORGRP operator command.
DISNEW: The system cannot create a new data set that is the first data set on a tape volume. It can read an existing data set, extend an existing data set, and create a new data set that is not the first on a tape volume. This condition can be changed by the VARY SMS,STORGRP operator command.
DISALL: The system cannot create or access data sets on any tape volume belonging to this storage group. This condition can be changed by the VARY SMS,STORGRP operator command.

Tape storage groups can be associated with one or more tape libraries, but all volumes of a multivolume data set must be contained within a single library and a single storage group. If one of the volumes required in a multivolume data set request resides outside of the library, the volume not in library installation exit (CBRUXVNL) can be used to direct the volume back into the library.

When a private volume is entered into a tape library and a storage group name is not provided, OAM sets the storage group name to blanks. The blank storage group name becomes the system default. The blank storage group is always enabled on all systems within the Storage Management Subsystem (SMS) complex.

It is a good idea for the storage administrator to assign all volumes in the blank storage group to other named storage groups as soon as possible. This allows an installation to take advantage of the storage group states (ENABLED, NOTCON, DISNEW, and DISALL). Also, the storage group name can be used to direct a volume to a particular library or libraries, rather than to any library within the SMS complex. This ensures that a volume is reentered into the appropriate library following the ejection of that volume, and provides a filter for reducing the length of the volume list displayed through ISMF.

Automated class selection (ACS) routines are storage-administrator-defined routines that automatically identify the storage class, storage group, and data class that are used for allocation of volumes for new tape data sets. The storage group definitions in the active control data set (ACDS) contain the names of the libraries to which these volumes may be assigned. During allocation, these library names are used to find the associated named collection of tape devices or device pool. The device pool names are then used during allocation to find the associated device numbers for the tape drives that may be used to satisfy the request.

Note:

For limitations on the number of device pools refer to Tape subsystem (device pool) limitation.
When both DASD and tape storage groups are eligible for a new allocation through the ACS routine, SMS defaults to DASD over the tape storage group, choosing the more efficient device. The user cannot influence this decision after the ACS routine has made the storage group selection.