During automatic primary space management, DFSMShsm can process a maximum of 15 volume migration tasks concurrently. This activity consists of the deletion of temporary data sets, deletion of expired data sets, and the release of unused and overallocated space, and migration. Each task processes its own separate user DASD volume. The storage administrator selects the maximum number of tasks that can run simultaneously, and specifies which days and the time of day the tasks are to be performed.

If a volume is system-managed, DFSMShsm uses the storage group threshold of occupancy as a measure of how much free space to provide. The volumes processed are those in storage groups having the automatic migration attribute. Storage groups can also be used to restrict the processing to a single system or a system group.

DFSMShsm manages each data set on a volume according to the management class attributes associated with the data set.

If a volume is non-system-managed, DFSMShsm manages each data set on a volume according to the attributes of the volume on which the data set resides.

Figure 1 shows the migration paths of data sets managed in system-managed and non-system-managed environments.

Figure 1. Automatic volume and secondary space management