freebsd man page for gcache

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 com-
     ponents, 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 vari-
     able.

     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
     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