/CACHE=(keyword[,...])
/NOCACHE
For disks, controls whether caching limits established at system
generation time are disabled or overridden. With the TAPE_DATA
option, enables write caching for the tape controller specified
(if the tape controller supports write caching).
The following table lists the keywords for this qualifier:
Keyword Description
DATA and Enable or disable Extended File Caching (XFC). To
NODATA enable XFC caching, you must specify the DATA (this
is the default value for /CACHE qualifier). To
disable XFC, specify NODATA. Note that /NOCACHE is
equivalent to /CACHE=NODATA.
EXTENT[=n] Enable or disable extent caching. To enable extent
and NOEXTENT caching, you must have the operator user privilege
(OPER) and you must specify n, the number of
entries in the extent cache. Note that NOEXTENT
is equivalent to EXTENT=0; both disable extent
caching.
FILE_ID[=n] Enable or disable file identification caching.
and NOFILE_ To enable file identification caching, you must
ID have the operator user privilege (OPER) and you
must specify n, the number of entries, as a value
greater than 1. Note that NOFILE_ID is equivalent
to FILE_ID=1; both disable file identification
caching.
LIMIT=n Specifies the maximum amount of free space in the
extent cache in one-thousandths of the currently
available free space on the disk.
QUOTA[=n] Enable or disable quota caching. To enable quota
and NOQUOTA caching, you must have the operator user privilege
(OPER) and you must specify n, the number of
entries in the quota cache. Normally n is set to
the maximum number of active users expected for a
disk with quotas enabled. Both NOQUOTA and QUOTA=0
disable quota file caching.
TAPE_DATA Enables write caching for a magnetic tape device
if the tape controller supports write caching. The
/CACHE qualifier is the default for mounting tape
devices. You must specify TAPE_DATA to enable write
caching. If the tape controller does not support
write caching, the keyword is ignored.
The write buffer stays enabled even after you
dismount the magnetic tape. To disable the write
buffer, mount a tape with the /NOCACHE qualifier.
If a tape supports compaction, then the default
is compaction, and caching is enabled. For tape
storage devices that support compaction, the
following command is valid:
$ MOUNT TAPE_DATA/FOREIGN/MEDIA=NOCOMPACTION/NOCACHE
WRITETHROUGH Disables the deferred write feature for file
headers. By default, this feature is enabled, which
improves the performance of applications, such as
PATHWORKS, that use it. The deferred write feature
is not available on Files-11 ODS-1 volumes.
NOTE
In a mixed-version OpenVMS cluster, an attempt to mount a
volume with /CLUSTER and /CACHE=[NO]DATA from a V8.4 system
fails on the pre-V8.4 systems (%MOUNT-W-RMTMNTFAIL) with
MOUNT-F-BADPARAM.
For more information on the restriction, see Enabling or
Disabling XFC While Mounting a Volume in the OpenVMS Version
8.4 New Features and Documentation Overview manual.
Used with the disk options, the /CACHE qualifier overrides
one or more of the present disk caching limits established at
system generation time. Used with the TAPE_DATA option, the
/CACHE qualifier enables write caching for the tape controller
specified.
If you do not specify the /CACHE qualifier and it is not implied
by the use of the qualifier /MEDIA_FORMAT=COMPACTION, caching is
enabled by default.
If you specify more than one option, separate them by commas
and enclose the list in parentheses. The options [NO]EXTENT,
[NO]FILE_ID, LIMIT, and [NO]QUOTA apply only to a disk device.
The option TAPE_DATA applies only to a tape device.
The /NOCACHE qualifier is effective only if compaction is
not enabled. If compaction is enabled (with the /MEDIA_
FORMAT=COMPACTION), caching is enabled by default.
If you specify /NOCACHE for a disk device, all caching is
disabled for this volume. Note that the /NOCACHE qualifier is
equivalent to /CACHE=(NOEXTENT, NOFILE_ID, NOQUOTA, WRITETHROUGH,
NODATA).
In the following command, NODATA is taken as default when you
supply the following qualifiers NOEXTENT, NOFILE_ID, NOQUOTA,
WRITETHROUGH (that is, XFC is disabled):
$ MOUNT/CACHE=(NOEXTENT, NOFILE_ID, NOQUOTA, WRITETHROUGH)
_$ $1$DGA0: FILES WORK
%MOUNT-I-MOUNTED, FILES mounted on $1$DGA0: (NODE)
In the following command, DATA is take as default (that is, XFC
is enabled):
$ MOUNT/CACHE=(FILE_ID=10)
_$ $1$DGA0: FILES WORK
%MOUNT-I-MOUNTED, FILES mounted on $1$DGA0: (NODE)
If you specify /NOCACHE for a magnetic tape device, the tape
controller's write cache is disabled for this volume.
Examples
The following command mounts an HSG80 Fibre Channel disk
device labeled FILES and assigns the logical name WORK. The
/CACHE qualifier enables an extent cache of 60 entries, a file
identification cache of 60 entries, and a quota cache of 20; it
disables writeback caching of file headers.
$ MOUNT/CACHE=(EXTENT=60,FILE_ID=60,QUOTA=20,WRITETHROUGH) -
_$ $1$DGA0: FILES WORK
%MOUNT-I-MOUNTED, FILES mounted on _$1$DGA0: (NODE)
The following command mounts the volume TAPE on device MUA0 and
instructs MOUNT to enable the tape controller's write cache for
MUA0:
$ MOUNT/CACHE=TAPE_DATA MUA0: TAPE
%MOUNT-I-MOUNTED, TAPE mounted on _NODE$MUA0:
The following command enables data cache (XFC) on a disk. The
/CACHE=DATA qualifier is the default value for a basic MOUNT
command:
$ MOUNT/CACHE=(DATA)
_$ $1$DGA0: FILES WORK
%MOUNT-I-MOUNTED, FILES mounted on $1$DGA0: (NODE)
The following command disables data cache (XFC) on a disk.
/NOCACHE qualifier is equivalent to /CACHE=(NODATA):
$ MOUNT/CACHE=(NODATA)
_$ $1$DGA0: FILES WORK
%MOUNT-I-MOUNTED, FILES mounted on $1$DGA0: (NODE)
The following command disables data cache that is, XFC and
metadata cache that is, XQP. /NOCACHE qualifier is equivalent
to /CACHE=(NODATA):
$ MOUNT/NOCACHE
_$ $1$DGA0: FILES WORK
%MOUNT-I-MOUNTED, FILES mounted on $1$DGA0: (NODE)