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GCACHE(8)               FreeBSD System Manager's Manual              GCACHE(8)

     gcache - control utility for CACHE GEOM class

     gcache create [-v] [-b blocksize] [-s size] name prov
     gcache configure [-v] [-b blocksize] [-s size] name
     gcache destroy [-fv] name
     gcache label [-v] [-b blocksize] [-s size] name prov
     gcache stop [-fv] name ...
     gcache clear [-v] prov ...
     gcache dump prov ...
     gcache list
     gcache status [-s name]
     gcache load [-v]
     gcache unload [-v]

     The gcache utility is used to control GEOM cache, which can speed up read
     performance by sending fixed size read requests to its consumer.  It has
     been developed to address the problem of a horrible read performance of a
     64k blocksize FS residing on a RAID3 array with 8 data components, where
     a single disk component would only get 8k read requests, thus effectively
     killing disk performance under high load.

     Caching can be configured using two different methods: ``manual'' or
     ``automatic''.  When using the ``manual'' method, no metadata are stored
     on the devices, so the cached device has to be configured by hand every
     time it is needed.  The ``automatic'' method uses on-disk metadata to
     detect devices.  Once devices are labeled, they will be automatically
     detected and configured.

     The first argument to gcache indicates an action to be performed:

     create       Cache the given devices with specified name.  This is the
                  ``manual'' method.  The kernel module geom_cache.ko will be
                  loaded if it is not loaded already.

     label        Cache the given devices with the specified name.  This is
                  the ``automatic'' method, where metadata are stored in every
                  device's last sector.  The kernel module geom_cache.ko will
                  be loaded if it is not loaded already.

     stop         Turn off existing cache device by its name.  This command
                  does not touch on-disk metadata!

     destroy      Same as stop.

     clear        Clear metadata on the given devices.

     dump         Dump metadata stored on the given devices.

     list         See geom(8).

     status       See geom(8).

     load         See geom(8).

     unload       See geom(8).

     Additional options:

     -f      Force the removal of the specified cache device.

     -v      Be more verbose.

     The following sysctl(8) variables can be used to control the behavior of
     the CACHE GEOM class.  The default value is shown next to each variable.

     kern.geom.cache.used_hi: 20

     kern.geom.cache.used_lo: 5

     kern.geom.cache.idletime: 5

     kern.geom.cache.timeout: 10

     kern.geom.cache.enable: 1

     kern.geom.cache.debug: 0
             Debug level of the CACHE GEOM class.  This can be set to a number
             between 0 and 3 inclusive.  If set to 0 minimal debug information
             is printed, and if set to 3 the maximum amount of debug
             information is printed.

     Exit status is 0 on success, and 1 if the command fails.

     geom(4), geom(8)

     The gcache utility appeared in FreeBSD 7.0.

     Ruslan Ermilov <>

FreeBSD 11.0-PRERELEASE         January 3, 2010        FreeBSD 11.0-PRERELEASE


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