1.\"- 2.\" Copyright (c) 2010 Edward Tomasz Napierala 3.\" All rights reserved. 4.\" 5.\" Redistribution and use in source and binary forms, with or without 6.\" modification, are permitted provided that the following conditions 7.\" are met: 8.\" 1. Redistributions of source code must retain the above copyright 9.\" notice, this list of conditions and the following disclaimer. 10.\" 2. Redistributions in binary form must reproduce the above copyright 11.\" notice, this list of conditions and the following disclaimer in the 12.\" documentation and/or other materials provided with the distribution. 13.\" 14.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24.\" SUCH DAMAGE. 25.\" 26.Dd September 28, 2026 27.Dt GCACHE 8 28.Os 29.Sh NAME 30.Nm gcache 31.Nd "control utility for CACHE GEOM class" 32.Sh SYNOPSIS 33.Nm 34.Cm create 35.Op Fl v 36.Op Fl b Ar blocksize 37.Op Fl s Ar size 38.Ar name 39.Ar prov 40.Nm 41.Cm configure 42.Op Fl v 43.Op Fl b Ar blocksize 44.Op Fl s Ar size 45.Ar name 46.Nm 47.Cm destroy 48.Op Fl fv 49.Ar name 50.Nm 51.Cm label 52.Op Fl v 53.Op Fl b Ar blocksize 54.Op Fl s Ar size 55.Ar name 56.Ar prov 57.Nm 58.Cm stop 59.Op Fl fv 60.Ar name ... 61.Nm 62.Cm clear 63.Op Fl v 64.Ar prov ... 65.Nm 66.Cm dump 67.Ar prov ... 68.Nm 69.Op Fl -libxo 70.Cm list 71.Nm 72.Op Fl -libxo 73.Cm status 74.Op Fl s Ar name 75.Nm 76.Cm load 77.Op Fl v 78.Nm 79.Cm unload 80.Op Fl v 81.Sh DESCRIPTION 82The 83.Nm 84utility is used to control GEOM cache, which can 85speed up read performance by sending fixed size 86read requests to its consumer. It has been developed to address 87the problem of a horrible read performance of a 64\~KiB blocksize FS 88residing on a RAID3 array with 8 data components, where a single 89disk component would only get 8\~KiB read requests, thus effectively 90killing disk performance under high load. 91.Pp 92Caching can be configured using two different methods: 93.Dq manual 94or 95.Dq automatic . 96When using the 97.Dq manual 98method, no metadata are stored on the devices, so the cached 99device has to be configured by hand every time it is needed. 100The 101.Dq automatic 102method uses on-disk metadata to detect devices. 103Once devices are labeled, they will be automatically detected and 104configured. 105.Pp 106The first argument to 107.Nm 108indicates an action to be performed: 109.Bl -tag -width ".Cm destroy" 110.It Cm create 111Cache the given devices with specified 112.Ar name . 113This is the 114.Dq manual 115method. 116The kernel module 117.Pa geom_cache.ko 118will be loaded if it is not loaded already. 119.It Cm label 120Cache the given devices with the specified 121.Ar name . 122This is the 123.Dq automatic 124method, where metadata are stored in every device's last sector. 125The kernel module 126.Pa geom_cache.ko 127will be loaded if it is not loaded already. 128.It Cm stop 129Turn off existing cache device by its 130.Ar name . 131This command does not touch on-disk metadata! 132.It Cm destroy 133Same as 134.Cm stop . 135.It Cm clear 136Clear metadata on the given devices. 137.It Cm dump 138Dump metadata stored on the given devices. 139.It Cm list 140See 141.Xr geom 8 . 142.It Cm status 143See 144.Xr geom 8 . 145.It Cm load 146See 147.Xr geom 8 . 148.It Cm unload 149See 150.Xr geom 8 . 151.It Fl -libxo 152Generate output via 153.Xr libxo 3 154in a selection of different human and machine readable formats. 155See 156.Xr xo_options 7 157for details on command line arguments. 158.El 159.Pp 160Additional options: 161.Bl -tag -width indent 162.It Fl f 163Force the removal of the specified cache device. 164.It Fl v 165Be more verbose. 166.El 167.Sh SYSCTL VARIABLES 168The following 169.Xr sysctl 8 170variables can be used to control the behavior of the 171.Nm CACHE 172GEOM class. 173The default value is shown next to each variable. 174.Bl -tag -width indent 175.It Va kern.geom.cache.used_hi : No 20 176.It Va kern.geom.cache.used_lo : No 5 177.It Va kern.geom.cache.idletime : No 5 178.It Va kern.geom.cache.timeout : No 10 179.It Va kern.geom.cache.enable : No 1 180.It Va kern.geom.cache.debug : No 0 181Debug level of the 182.Nm CACHE 183GEOM class. 184This can be set to a number between 0 and 3 inclusive. 185If set to 0 minimal debug information is printed, and if set to 3 the 186maximum amount of debug information is printed. 187.El 188.Sh EXIT STATUS 189Exit status is 0 on success, and 1 if the command fails. 190.Sh SEE ALSO 191.Xr geom 4 , 192.Xr xo_options 7 , 193.Xr geom 8 194.Sh HISTORY 195The 196.Nm 197utility appeared in 198.Fx 7.0 . 199.Sh AUTHORS 200.An Ruslan Ermilov Aq Mt ru@FreeBSD.org 201