VMS Help  —  MOUNT  Qualifiers  /CACHE
       /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 (default)   Enable or disable Extended File Caching (XFC). To
    and 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_ID    To enable file identification caching, you must
                     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)
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