The COMPRESS command compresses partitioned data sets on a specified volume. Compressing (degassing) removes unused space between members in a partitioned data set. Depending on the filtering criteria that you specify, you can compress either all or some of the partitioned data sets. This command is useful for compressing system partitioned data sets before you apply maintenance (to avoid certain space-related abends).

Restriction: You must not compress data sets that contain DFSMSdss or IEBCOPY executable code.

The actual PDS compression is done on the existing volume using the IEBCOPY utility. To prevent loss of data if the system or IEBCOPY abnormally ends during the processing, back up volumes or data sets that meet the filtering criteria before you use the COMPRESS command.

The COMPRESS command cannot process partitioned data sets that:

• Are unmovable
• Have no directory