Volume serial number

You are not required to specify volume serial numbers for unlabeled output tapes. If none is specified, the mount message directs the operator to mount a scratch tape.

DFSMSrmm prevents the use of unlabeled scratch tapes because there is no way to tell which volume is mounted or to manage them without operator intervention.

If you request a specific volume, the operating system uses the specified volume serial number for mounting messages, for cataloging, and for passing the volumes to other job steps.

If you do not request a specific volume, the system cannot obtain the actual serial number of the volume that is mounted. In this case, the system generates a volume serial number and assigns it to the volume. These volume serial numbers are generated in the form Lxxxyy, where:

xxx: is a number the open routine increments (by one) each time an output data set is opened on a nonspecified unlabeled volume. If more than one data set is created on the same volume, this number is increased only when the first data set is opened.
yy: is set to 00 by the open routine. The EOV routine increments this number (by one) each time an end-of-volume condition occurs. In this way, each volume of a multivolume data set is assigned a different volume serial number.

If a data set is to be cataloged, you should specify the volume serial numbers for all the volumes required. This prevents different data sets residing on different volumes from being cataloged with identical volume serial numbers, which could result in the mounting of wrong volumes.