You can specify the amount of space required in blocks, records, tracks, or cylinders. When creating a DASD data set, specify the amount of space needed explicitly by using the SPACE parameter, or specify the amount of space implicitly by using the information available in a data class. The data class is not used if SMS is inactive at the time of your allocation.

The system can use a data class if SMS is active even if the data set is not SMS managed. For system-managed data sets, the system selects the volumes. Therefore, you do not need to specify a volume when you define your data set.

If you specify your space request by average record length, space allocation is independent of device type. Device independence is especially important to system-managed storage.