You are not required to specify volume serial numbers for output tapes, unless you are extending an existing tape data set. Serial numbers are required when the processing method is EXTEND or OUTINX or it is OUTPUT with DISP=MOD. If no number is specified, the mount message directs the operator to mount a scratch tape. The system obtains the volume serial number from the VOL1 label and records it in the JFCB and the UCB.

If you choose to specify the volume serial number, the system compares it with the volume serial number shown in the VOL1 label. If the serial numbers match, then the system resets a mount switch in the UCB to indicate that volume mounted is verified. The mount switch is initially set when the mount message is issued to the operator. If the serial numbers do not match, the system may give the operator the option of having the label rewritten with the serial number of the volume requested. This will occur if the tape is not password protected, is not date protected, and is not a checkpoint/restart volume. Otherwise, the system rejects the tape and issues another mount message. DFSMSrmm prevents an incorrect tape from being used and the label being rewritten.