During automatic primary space management:
- All DFSMShsm hosts delete temporary data sets and expired data
sets from the DFSMShsm-managed volumes they are processing. This is
done under the control of the management class associated with each
data set on the volume or the expiration date contained in the data
set's volume table of contents (VTOC) entry.
- Under control of the data set management classes, all DFSMShsm
hosts release unused allocated space in physical sequential, partitioned,
and extended format virtual storage access method (VSAM) data sets.
- During data set and volume processing, fast subsequent migration
reconnects eligible data sets to the ML2 tape from which they were
most recently recalled.
- Under the extent reduction function, all DFSMShsm hosts also reduce
the number of extents of physical sequential, partitioned, and direct
access data sets that have exceeded a specified number of extents.
During the process of extent reduction, they also release any unused
space in the data sets and compress partitioned data sets.
- Data sets that are eligible for a class transition
are transitioned. If a data set is eligible for both a class transition
and migration, the data set will only be migrated. This prevents the
data set from being moved from one level 0 volume to another for a
transition, only to be later migrated to a migration volume.
- Data sets that are eligible for migration are migrated.
Primary space management continues until the SMS-managed volumes
have the specified amount of free space. However, if deletion of expired
data sets, fast subsequent migration, and space reduction of the remaining
data sets achieves the specified volume free space low threshold,
no actual data sets are moved.
If data sets are to be migrated during primary space management,
they will be migrated in compacted form if possible. Data sets expected
to be smaller than 110 KB (where 1 KB is 1024 bytes) after
they are compacted are candidates for small data set packing (SDSP)
if enabled.