Managing Temporary Data

Recommendation: After you activate SMS, select temporary data sets for migration to system-managed storage. Managing temporary data sets during this phase of the implementation enables you to gain experience with DFSMS functions. Temporary data sets are easy to identify and recreate, and do not require availability management. The following are benefits of system-managed temporary data sets:

Both temporary VSAM and non-VSAM data sets are supported.
Temporary data sets are automatically deleted by DFSMShsm, thus supporting efficient space management.
Temporary data sets left by the system because of abnormal end-of-job are deleted by DFSMShsm during space management.
Temporary data sets can be allocated on VIO or system-managed storage volumes.
Using system-managed temporary data eliminates the need for dedicated public or temporary volumes, and frees volumes for permanent data sets.
Temporary data sets can be directed to VIO based on data set size and usage, improving performance by directing I/O to your processor's central or expanded storage.
VIO data sets are backed by auxiliary storage as paging data sets.
Temporary data set access to VIO can be restricted, based on the RACF® variables, &USER and &GROUP.
RACF-related ACS READ/WRITE variables, &USER and &GROUP, can be interrogated in your ACS routine to limit access to VIO.

Temporary data sets are created and deleted within the same job, job step, or terminal session. No entries are made in the basic catalog structure (BCS) for these data sets, but system-managed VSAM data sets do have VVDS entries. Both VSAM and non-VSAM data sets have VTOC entries. The data set name for temporary data is either omitted or is a single qualifier with && or && at the beginning. When the DSNAME is omitted, the system generates a name that begins with SYS and includes the Julian date and time.

When you code request temporary data set allocation, the ACS read-only variable data set type, &DSTYPE, is set to TEMP. The storage class ACS routine determines whether to allocate these data sets to VIO or to volumes in a pool storage group category depending on the data set usage and size. During automatic space management, DFSMShsm automatically deletes system-managed temporary data sets that remain on a volume after an abnormal end of job or system failure. Figure 1 shows how DFSMShsm allocates and manages temporary data sets.

Figure 1. System-Managed Temporary Data

The following major tasks are required for system-managed temporary data sets:

Review the planning considerations
Define SMS storage classes and groups
Create ACS routines
Test the ACS routines
Initialize DASD volumes for LARGExx and PRIMExx storage groups
Reactivate the configuration