Extension to Another DASD Volume

The system attempts to extend to another DASD volume if all of the following conditions exist:

The current volume does not have the secondary space amount available, or the data set reached the extent limit for that type of data set, or the application program issued the FEOV macro.
The volume count has not yet been reached. For a system-managed data set, the volume count was determined when the data set was created (DISP=NEW) and is the largest of the volume count (VOL=(,,,nn)), the number of volumes coded with the VOL parameter, and the unit count (UNIT=(xxxx,nn)).
For either system-managed or non-system-managed data sets, the volume count can come from the data class. The volume count can be increased after data set creation with the IDCAMS ADDVOL command.
The dynamic volume count has not been reached for a system-managed data set. You can define the Space Constraint Relief and Dynamic Volume Count attributes in the data class. If Space Constraint Relief=YES, you can specify a dynamic volume count from 1 to 59 for SMS to extend a data set automatically to another volume or volumes. For more information, see z/OS DFSMSdfp Storage Administration.
A secondary allocation amount is available. This can come from the data class when the data set was created even if the data set is not system managed. When the data set is created with DISP=NEW or IDCAMS DEFINE, the secondary amount permanently overrides data class for the data set. For a non-VSAM data set the above two sources of the secondary amount can be overridden temporarily with DISP other than NEW.

Note: After a multivolume data set is unable to extend on the current volume and the data set is extended to a new volume, then all previous volumes can no longer be selected for future extensions.