gcache man page on FreeBSD

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

NAME
     gcache — control utility for CACHE GEOM class

SYNOPSIS
     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]

DESCRIPTION
     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.

SYSCTL VARIABLES
     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 informa‐
	     tion is printed.

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

SEE ALSO
     geom(4), geom(8)

HISTORY
     The gcache utility appeared in FreeBSD 7.0.

AUTHORS
     Ruslan Ermilov ⟨ru@FreeBSD.org⟩

BSD				January 3, 2010				   BSD
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