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