Purpose of space management
Space management is the function of DFSMShsm that allows you to
keep DASD space available for users in order to meet the service-level
objectives for your system. The purpose of space management is to
manage your DASD storage efficiently. To do this, space management
automatically and periodically performs functions that (1) move low-activity
data sets from user-accessible volumes to DFSMShsm volumes, (2) move data sets from one class of user-accessible
volumes to another class of user-accessible volumes, and (3)
reduce the space occupied by data on both the user-accessible volumes
and the DFSMShsm volumes. The DFSMShsm space management functions
are:
- Automatic primary space management of DFSMShsm-managed volumes,
which includes:
- Deletion of temporary data sets
- Deletion of expired data sets
- Release of unused, over-allocated space
- Migration to DFSMShsm-owned migration volumes
- Transitions between different classes of user-accessible volumes
- Automatic secondary space management of DFSMShsm-owned volumes,
which includes:
- Migration level cleanup, including deletion of expired migrated data sets and some migration control data set (MCDS) records
- Moving migration copies from migration level 1 (ML1) to migration level 2 (ML2) volumes
- Event-driven migration and transitions, initiated when a DFSMShsm-managed volume exceeds a specified threshold
- Automatic recall of user data sets back to DASD volumes
- Space management by command
- Space-saving functions, which include:
- Small data set packing
- Partitioned data set compression
- Data compaction and zEDC compression
- Data set reblocking