SMS allows the system resources manager (SRM) to select a DASD volume from the primary volume list if the IART value is 0 or unspecified. SRM volume selection is ideally suited for batch jobs.

You can allow SMS, instead of SRM, to select a DASD volume by assigning a storage class with a nonzero IART value. In this case, none of the eligible volumes is placed on the primary list; all of the eligible volumes are placed only on the secondary or tertiary list. SMS uses the randomizing technique, for example, so as not to always select the volume that has the most free space.

See SMS volume selection for data set allocation for further information on SMS volume selection.