SMS classes

With SMS, a new data set can have one or more of the following three classes:

Data class contains the data set attributes related to the allocation of the data set, such as LRECL, RECFM, SPACE, and TRACKS.
Storage class contains performance and availability attributes related to the storage occupied by the data set. A data set that has a storage class assigned to it is defined as an "SMS-managed" data set.
Management class contains the data set attributes related to the migration and backup of the data set, such as performed by DFSMShsm, and the expiration date of the data set. A management class can be assigned only to a data set that also has a storage class assigned.

All of the preceding classes are defined by the storage administrator at your installation. The administrator writes the automatic class selection (ACS) routines that SMS uses to assign the classes to a new data set.

The DATACLAS, MGMTCLAS, and STORCLAS operands of the ALLOCATE command simplify the process of allocating a new data set. For example, assigning the DATACLAS operand to a data set keeps you from having to specify all the attributes of the data set on the ALLOCATE command. If you assign a storage class (STORCLAS) to a data set, you do not have to specify a volume serial number (VOLUME) or a unit type (UNIT).

If you do not specify DATACLAS, MGMTCLAS, and STORCLAS or the overriding attributes (DSORG, RECFM, LRECL, and so forth), the system assumes the defaults that the storage administrator defined through the ACS routines. The ACS routines can either change or retain the specified data set attributes. You can specify both a class attribute and an overriding attribute, such as DATACLAS and SPACE. The system uses SPACE as the storage value and the allocation attributes associated with the name specified on DATACLAS.

Note: You must explicitly allocate a new SMS-managed data set with a disposition of NEW.