Requesting and using scratch pools

DFSMSrmm system-based scratch pooling is always available for you to use, however, you cannot use it for automated system-managed tape. To use exit-selected scratch pooling, install the sample EDGUX100 exit module on your system and customize it to set a specific pool for a non-specific volume request. See Using DFSMSrmm installation exits for information about how to use the EDG_EXIT100 installation exit.

DFSMSrmm updates the mount message and drive display with the appropriate pool prefix, pool name, or storage group name. DFSMSrmm validates the mounted scratch volume against the selected scratch pool prefix, pool name, or storage group during OPEN processing.

You can set up DFSMSrmm to satisfy each request for a new scratch tape in one of these ways:

Set up a default pool using the EDGRMMxx parmlib OPTION VLPOOL command. DFSMSrmm uses the VLPOOL definitions to select a default DFSMSrmm pool by using DFSMSrmm system-based pooling when you have not set up other pools. DFSMSrmm sets a pool prefix and a pool name if a specific pool is selected. Set up DFSMSrmm system-based scratch pooling using the DFSMSrmm VLPOOL command with the SYSID operand. This method allows you to control which scratch pools can be used based on the system on which the volumes are used. This enforces pooling based on VLPOOL prefix pools. DFSMSrmm uses the DFSMSrmm system-based scratch pooling when you do not select any other method.
Use ACS routines for scratch pooling based on tape storage group names. Using ACS processing to set a storage group name overrides all other pool selection methods. DFSMSrmm provides support for non-system-managed tape and for system-managed manual tape libraries. This support enables pooling at the individual volume level. You assign a storage group name to each volume by using DFSMSrmm TSO subcommands or by using pooling information that you define with the DFSMSrmm EDGRMMxx parmlib VLPOOL command. See Using SMS tape storage groups for DFSMSrmm scratch pooling for additional information. DFSMSrmm calls ACS routines passing environment information, including the pool identified by DFSMSrmm system-based pooling. The ACS routine can optionally set a storage group name, which overrides the DFSMSrmm system-based pool.
Customize the sample EDGUX100 exit module that is described in Using DFSMSrmm installation exits to select a pool prefix. You can use information in the system to determine which pool to use. DFSMSrmm calls the EDG_EXIT100 installation exit if ACS processing does not return a storage group name. The EDG_EXIT100 installation exit can return a pool prefix value that overrides the DFSMSrmm system-based pool. The pool name is set based on the selected pool prefix.
Use pre-ACS processing to obtain the DFSMSrmm system-based pool or the EDG_EXIT100 installation exit pool prefix as an input value to the ACS routines in the MSPOOL read-only variable. During pre-ACS processing, DFSMSrmm does not make the RMMPOOL environment call to the ACS routine. During pre-ACS processing for new allocations:
- DFSMSrmm uses the VLPOOL definitions to select a default DFSMSrmm pool using DFSMSrmm system-based pooling. DFSMSrmm sets a pool prefix if a specific pool is selected.
- DFSMSrmm calls the EDG_EXIT100 installation exit to obtain a pool prefix value. If a pool prefix value is returned, the pool prefix value returned by the EDG_EXIT100 installation exit overrides the DFSMSrmm selected pool.
- DFSMSrmm returns the selected value in the MSPOOL read-only variable if the MSPOOL variable is not already set by the pre-ACS exit.