Releasing unused space in data sets

The RELEASE command releases allocated but unused space from all sequential, partitioned, and extended-format data sets that you select with INCLUDE, EXCLUDE, or BY criteria. For an explanation of these criteria, see DFSMSdss filtering—choosing the data sets you want processed. DFSMSdss selects only data sets that have space that can be released. You can also use ISMF to build a list of data sets based on the amount of unused space and to invoke DFSMSdss to release the unused space in them.

Exclude data sets whose last block pointer in the data set VTOC entry is not maintained in the VTOC by using the EXCLUDE keyword. This can occur if you use an access method other than BSAM, QSAM, BPAM, or VSAM. DFSMSdss does not release space for data sets whose last block pointer in the data set entry is 0.

The following options can help you use the release function more effectively:

MINSECQTY(n): Allows you to specify that space not be released unless the user’s secondary allocation is greater than or equal to n. In this way, you ensure that the user can still add to the data set after the release. The default value for n is 1.
MINTRACKSUNUSED(n): Allows you to specify that space not be released unless the number of unused tracks is greater than or equal to n. Without MINTRACKSUNUSED, space is released if the data set has one or more unused tracks.

Note: When space in a data set is released, all unused space is released, not just the amount beyond the minimum unused (as specified by MINTRACKSUNUSED).

To protect the user, DFSMSdss does not release any space in a data set if:

The data set has the maximum number of used extents. A data set with the maximum number of allocated extents but fewer than the maximum number of used extents will have the unused space released.
The cylinder-allocated data set has unused tracks but not an entire unused cylinder.
The data set’s name begins with SYS1, unless the PROCESS(SYS1) keyword is specified. To limit the use of PROCESS, you need to set up a RACF® FACILITY class profile.