Technical data

Managing Storage Media
9.9 Dismounting Volumes and Volume Sets
9.9 Dismounting Volumes and Volume Sets
When you finish processing the files or data on a disk or tape volume, use the
DISMOUNT command to explicitly dismount a single volume or an entire volume
set.
Use the following format when you enter the DISMOUNT command:
DISMOUNT device-name
where:
device-name Name of the device containing the volume—either a logical name or a
physical name. If you specify a physical name, the controller defaults
to A and the unit defaults to 0.
If the volume currently mounted on the device is a member of a disk
or tape volume set, all volumes in the set are dismounted unless you
specify the /UNIT qualifier.
You can dismount a volume on a local node or on all the nodes throughout a
cluster.
Before dismounting a volume or volume set, the DISMOUNT command checks for
conditions that prevent the dismount from completing:
• Installed swap and page files
• Installed images
• Devices spooled to the volume
• Open user file (any files not falling into one of the first three groups)
If none of these conditions is found, the volume is marked for dismount. If any
of these conditions exists, the DISMOUNT command does not mark the volume
for dismount but, instead, displays error messages indicating the conditions that
exist, the number of instances of each condition, and the fact that the volume
cannot be dismounted.
If you attempt to dismount the system disk after it has been mounted shared, you
may see a message such as the following one, even if there are no user files open:
%DISM-W-CANNOTDMT, AXP27$DKA300: cannot be dismounted
%DISM-W-USERFILES, 1 user file open on volume
The message occurs because the file DISMOUNT.EXE is opened as a ‘‘user’’ file in
the course of the dismount operation. To eliminate the error message, install the
file DISMOUNT.EXE.
In some cases, you might want to mark a volume for dismount even though files
are open on the volume. Marking the volume for dismount prevents users from
opening any new files, thereby allowing activity to wind down. You can use the
qualifier /OVERRIDE=CHECKS to mark the volume for dismount even if files are
open.
Dismounting with Cached Information
As a performance enhancement, the system stores volume information in memory,
including information about free space on a disk volume, file identifications,
quota file entries, and file headers. This storing of information is called caching.
Cached information can include blocks allocated but not yet in a file, or files
created but not yet in a directory.
Managing Storage Media 9–57