Manual Pages  — GCACHE

gcache – control utility for CACHE GEOM class

SYNOPSIS DESCRIPTION SYSCTL VARIABLES EXIT STATUS SEE ALSO HISTORY AUTHORS

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]

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.

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

The gcache utility appeared in FreeBSD 7.0 .

Ruslan Ermilov <Mt ru@FreeBSD.org>