Technical data

Managing Storage Media
9.9 Dismounting Volumes and Volume Sets
You can access all the files that precede the file whose file-trailer labels have not
been written. However, you cannot access the file that does not have file-trailer
labels.
9.9.1.2 Dismounting Allocated Devices
If the device you are dismounting was allocated with an ALLOCATE command,
it remains allocated after you dismount it with the DISMOUNT command. If
the device was implicitly allocated with the MOUNT command, the DISMOUNT
command deallocates it.
9.9.1.3 Using DISMOUNT Command Qualifiers
The following table explains the /UNIT and /NOUNLOAD qualifiers.
Qualifier Description
/UNIT Explicitly dismounts a single volume in the volume set without dismounting the entire
set. (By default, the system dismounts all the volumes in the set when you explicitly
dismount a single volume in a volume set.)
Using this qualifier dismounts a volume but does not ‘‘unbind’’ the volume from the
volume set; if you remount the volume, it becomes part of the volume set again.
/NOUNLOAD Overrides the default automatic unloading of your volume from the drive. With this
qualifier, your volume is logically dismounted from the drive; however, the volume
remains physically loaded on the drive.
If you use this qualifier to dismount a tape volume, the volume remains loaded on the
tape drive and the tape reel is rewound to the BOT mark.
Using this qualifier can save time and eliminate unnecessary handling of a volume if
you plan to remount or reinitialize a volume you are dismounting.
Example
The following example shows how to use the DISMOUNT command. The example
uses the /NOUNLOAD qualifier.
$ DISMOUNT/NOUNLOAD MUA1:
In this example, the tape volume is logically dismounted and remains loaded on
the MUA1: device. Also, the tape reel is rewound to the beginning-of-tape mark.
The operating system returns you to DCL level.
9.9.2 Dismounting a Volume Set
Use the DISMOUNT command to dismount an entire volume set. If you explicitly
dismount any volume in a disk or tape volume set, the entire volume set is
dismounted. For example, if you have a volume set that consists of DUA3:
and DUA4: and you enter the following command, the entire volume set is
dismounted:
$ DISMOUNT DUA3:
9.9.3 Dismounting Foreign Volumes
You also use the DISMOUNT command to dismount foreign volumes. The
following command dismounts a volume that has been mounted with the
/FOREIGN qualifier on the DUA0: device:
$ DISMOUNT DUA0:
In this example, the volume that had been mounted with the /FOREIGN qualifier
on DUA0: is dismounted and automatically unloaded. The system returns you to
DCL level.
Managing Storage Media 9–59