When you use access method services commands, you must identify data sets and volumes. Data sets must be identified when they are accessed. Volumes must be identified when the system accesses the volume table of contents (VTOC), allocates or releases space or accesses a VSAM volume data set (part of the catalog).

VSAM data sets or volumes can be identified through the ALLOCATE command, through job control language (JCL), or by the data set name or volume serial number within the command that requires the data set or volume for its execution. If you do not use JCL or the ALLOCATE command, an attempt is made to dynamically allocate the data set or volume as required.

Under the SMS, you should not explicitly identify volumes. The system identifies the necessary volumes when a storage class is assigned to the data set. You can allocate your data set to a specific volume only if your storage administrator has set GUARANTEED SPACE=YES in the storage class assigned to your data set. See z/OS DFSMSdfp Storage Administration for further information about SMS volume selection.