With the exception of tape data sets, a data set is system-managed if it has a storage class. When you assign a storage class to a system-managed DASD data set, SMS places the storage class name in both the BCS and the VVDS catalog entries of the data set.

To satisfy the availability requirements of critical data sets, SMS selects a volume that can provide data access even in the event of a single device failure. For example, this can be satisfied by a device that has dual copy active or that is an array DASD.

If you need to access data sets while they are being copied or backed up, you can place them on volumes that support concurrent copy, virtual concurrent copy, or FlashCopy®.

With storage classes, you can also specify whether a data set is referenced primarily in the read or write mode.

For information on establishing dual copy volumes and enabling or disabling cache functions, see SETCACHE functions and device information. In this section, you can also find information on IBM® storage control units that support these features.

Tape data sets are not SMS-managed, even though you can assign them a storage class. Only tape volumes are SMS-managed. Therefore, none of the storage class attributes apply to tape data sets. Tape data sets do not have to be cataloged. If you do catalog a tape data set, the SMS information, such as data classes, storage classes, and management classes, is not saved in the catalog. You can direct tape data sets with a storage class to an SMS-managed tape volume by using the storage group ACS routine.