Releasing Unused Space from a DASD Data Set Using PARTREL

DADSM supports the release of unused space that is allocated to sequential or partitioned data sets, PDSEs, sequential extended-format data sets, and VSAM extended format data sets.The partial release function is called when:

The data set is closed (if the RLSE subparameter of SPACE was specified on its DD statement or the storage administrator specified an appropriate value for the partial release option in the management class definition).
A restart is processing from a checkpoint taken before the data set was extended.
DFSMShsm performs a space management cycle and an appropriate value is specified in the management class definition.
A PARTREL macro is issued.

For an extended address volume, partial release processing will release space on multicylinder unit boundaries when the last used track is in an extent in cylinder-managed space. For VSAM striped data sets where at least one stripe is on an extended address volume, partial release processing will ensure the stripes remain the same size. For these reasons, it is possible that the high allocated track after the release may be larger than the last used track or that no space could be released.