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.\" Copyright (c) 2010 Edward Tomasz Napierala
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.Dd January 3, 2010
.Dt GCACHE 8
.Os
.Sh NAME
.Nm gcache
.Nd "control utility for CACHE GEOM class"
.Sh SYNOPSIS
.Nm
.Cm create
.Op Fl v
.Op Fl b Ar blocksize
.Op Fl s Ar size
.Ar name
.Ar prov
.Nm
.Cm configure
.Op Fl v
.Op Fl b Ar blocksize
.Op Fl s Ar size
.Ar name
.Nm
.Cm destroy
.Op Fl fv
.Ar name
.Nm
.Cm label
.Op Fl v
.Op Fl b Ar blocksize
.Op Fl s Ar size
.Ar name
.Ar prov
.Nm
.Cm stop
.Op Fl fv
.Ar name ...
.Nm
.Cm clear
.Op Fl v
.Ar prov ...
.Nm
.Cm dump
.Ar prov ...
.Nm
.Cm list
.Nm
.Cm status
.Op Fl s Ar name
.Nm
.Cm load
.Op Fl v
.Nm
.Cm unload
.Op Fl v
.Sh DESCRIPTION
The
.Nm
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.
.Pp
Caching can be configured using two different methods:
.Dq manual
or
.Dq automatic .
When using the
.Dq 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
.Dq automatic
method uses on-disk metadata to detect devices.
Once devices are labeled, they will be automatically detected and
configured.
.Pp
The first argument to
.Nm
indicates an action to be performed:
.Bl -tag -width ".Cm destroy"
.It Cm create
Cache the given devices with specified
.Ar name .
This is the
.Dq manual
method.
The kernel module
.Pa geom_cache.ko
will be loaded if it is not loaded already.
.It Cm label
Cache the given devices with the specified
.Ar name .
This is the
.Dq automatic
method, where metadata are stored in every device's last sector.
The kernel module
.Pa geom_cache.ko
will be loaded if it is not loaded already.
.It Cm stop
Turn off existing cache device by its
.Ar name .
This command does not touch on-disk metadata!
.It Cm destroy
Same as
.Cm stop .
.It Cm clear
Clear metadata on the given devices.
.It Cm dump
Dump metadata stored on the given devices.
.It Cm list
See
.Xr geom 8 .
.It Cm status
See
.Xr geom 8 .
.It Cm load
See
.Xr geom 8 .
.It Cm unload
See
.Xr geom 8 .
.El
.Pp
Additional options:
.Bl -tag -width indent
.It Fl f
Force the removal of the specified cache device.
.It Fl v
Be more verbose.
.El
.Sh SYSCTL VARIABLES
The following
.Xr sysctl 8
variables can be used to control the behavior of the
.Nm CACHE
GEOM class.
The default value is shown next to each variable.
.Bl -tag -width indent
.It Va kern.geom.cache.used_hi : No 20
.It Va kern.geom.cache.used_lo : No 5
.It Va kern.geom.cache.idletime : No 5
.It Va kern.geom.cache.timeout : No 10
.It Va kern.geom.cache.enable : No 1
.It Va kern.geom.cache.debug : No 0
Debug level of the
.Nm 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.
.El
.Sh EXIT STATUS
Exit status is 0 on success, and 1 if the command fails.
.Sh SEE ALSO
.Xr geom 4 ,
.Xr geom 8
.Sh HISTORY
The
.Nm
utility appeared in
.Fx 7.0 .
.Sh AUTHORS
.An Ruslan Ermilov Aq Mt ru@FreeBSD.org