Tape multi-volume considerations

When a tape volume is premounted using the MOUNT command, the system will not dismount that volume even if additional volumes are required for the data set. Instead, an additional tape drive or drives will be allocated for the additional volumes. For example, assume that dataset BACKUP.SMFDATA.DAILY already resides on tape volume 123456, which is premounted using the MOUNT command.

//DUMPOUT  DD  DSNAME=BACKUP.SMFDATA.DAILY,DISP=(MOD,KEEP),
//             VOL=(,,,40)      

If a job has a DD statement with a volume count of 40, it will cause the system to allow for 39 scratch volumes. But since volume 123456 may not be dismounted, the system will allocate an additional tape drive for the scratch volumes, even if the data set does not extend onto any additional volumes.

Note also that the system will issue a mount message for the premounted volume. However, the mount message will only appear on the job's JES Job Log and in the SYSLOG. It will not appear on the operator's console.