GCACHE(8) |
FreeBSD 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 ... |
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 information is printed.
EXIT STATUS
Exit status is 0 on success, and 1 if the command fails.
HISTORY
The
gcache utility appeared in
FreeBSD 7.0.
AUTHORS
Ruslan Ermilov <ru@FreeBSD.org>