Pooling overview

A pool is a group of rack numbers or volumes that share a common prefix. In DFSMSrmm, there are two categories of pools: rack and scratch.

A rack pool is shelf space that can be assigned to hold any volumes. Although you can add scratch volumes to these pools, you cannot normally use these volumes to satisfy non-specific mount requests. A rack pool cannot be used with the DFSMSrmm system-based scratch pooling. Rack pools can perform these functions:

Hold volumes that are temporarily brought into the library but will be returned to the owner after a period of time
Hold customer, foreign tapes, and software product volumes
Contain scratch volumes for use with DFSMSrmm exit-selected scratch pooling

A scratch pool is shelf space assigned to hold volumes for use with the DFSMSrmm system-based scratch pooling. The volumes assigned to this shelf space can be used to satisfy scratch requests as long as the volumes are in scratch status. Once the volume has been written to, it becomes a volume with MASTER status, until the volume is returned to scratch status. The volume remains in the same DFSMSrmm system based scratch pool, in that it occupies the same shelf space regardless of status.

The scratch volumes in a system-managed tape library can be from one or more pools. DFSMSrmm does not provide pool selection or validation for volumes in an automated tape library because ACS routines use storage class and storage group to make allocation decisions, and the library manager picks a scratch volume. DFSMSrmm provides pool validation for volumes that reside in a manual tape library. You can pool by storage group, exit-selected pool prefix, or DFSMSrmm system-based pooling when using manual tape libraries.

DFSMSrmm allows you to use these basic types of pooling:

Pools of shelf space that are based on rack number prefixes. Each range identifies characteristics like management criteria and media name. Use shelf space pools to store volumes that do not match your installation-selected volume ranges and to store duplicate volumes. Define shelf space pools by using the DFSMSrmm EDGRMMxx VLPOOL command that is described in Defining pools: VLPOOL.
Pools of volumes that are based on the volume serial number prefix. These volumes do not have a rack number or the rack number matches the volume serial number. Each range identifies characteristics like management criteria and media name. Define volume prefix pools by using the DFSMSrmm EDGRMMxx VLPOOL command that is described in Defining pools: VLPOOL.
Scratch pools. These can be one or more pools of volumes. Scratch pools can be based on name, SMS storage group, prefix, or system. You define scratch pools by using the SYSID, PREFIX, and NAME operands of the DFSMSrmm EDGRMMxx VLPOOL command that is described in Defining pools: VLPOOL.
Storage groups. When you pool by storage group and use SMS ACS processing to assign a storage group to a tape data set, or the volume is in a system-managed manual tape library, DFSMSrmm ensures that a volume from the correct storage group is mounted. The storage group can be the same across multiple VLPOOL entries. You can use storage group for scratch pooling for system-managed manual tape libraries and non-system managed tape. Volumes that have been assigned storage group names cannot be used to satisfy scratch mount requests that do not request volumes from a specific storage group unless the mount request is in a manual system-managed tape library.

Pools can be used in these ways:

Adding shelf space - DFSMSrmm matches the rack number prefix to the most specific VLPOOL prefix. The rack media name is taken from the matching VLPOOL entry.
Adding volumes - You can optionally specify RACK or POOL operands to override default processing. Default processing matches the volume serial number prefix to the most specific VLPOOL prefix. If a rack number is found that matches the volume serial number and the specified media name, the volume is stored in the matching shelf pool. If no rack number is found, the volume is in a volume pool. When adding a volume you can specify a storage group name so that the volume can be in a specific scratch pool. If no storage group is specified by the command, DFSMSrmm checks to see if the matching VLPOOL NAME is a storage group, and uses that value as the storage group name. In this case, the scratch pool matches the volume pool.
Managing access to a volume - For system-managed tapes in a manual tape library, DFSMSrmm validates the mounted volume for the requested pool. You can use the installation exit to ignore the storage group pool and use DFSMSrmm system-based scratch pooling described in Using storage group for manual tape library pooling.
Defining actions that should be taken when volumes are ready for release - You can define release actions for volumes on the pool level that might not already be set for individual volumes. For example, you can set the NOTIFY options so that DFSMSrmm sets notification on the release action if it is not already on at the volume level.
Selecting scratch pools for new tape data sets - For system-managed tape, SMS ACS processing assigns a storage group. DFSMSrmm uses the storage group name to pool the volumes into a scratch pool. For non-system managed tape, DFSMSrmm calls SMS ACS processing to allow a storage group to be assigned. If no storage group is assigned, the EDG_EXIT100 installation exit is used.

When you pool by pool prefix, selected by EDG_EXIT100 or by SYSID, and the VLPOOL prefix has an associated NAME, DFSMSrmm uses the pool name for mount messages and drive displays but always validates mounted volumes by using the pool prefix and SYSID. Multiple VLPOOL entries can have the same SYSID values and the same NAME values.