GCACHE -- what's it for?

[Gary Palmer]

On Mon, Dec 15, 2008 at 09:06:33PM -0700, Geoff Fritz wrote:
> I noticed the presence of the geom_cache module recently.  Very little
> available in the archives on what it's used for.
> 
> Found a post by pjd@ with a link to a tarball containing a man page:
> 
> "The gcache utility is used for setting up a clean cache in front of the IDE
> controller on one disk."
> 
> (btw, where do I post to get this man page included in the release?
> freebsd-doc?  I'm running 7.1-RC1 and the man page is absent.)
> 
> I set up a test device with it, and noticed that the disk did a lot of
> thrashing when it was being written to, moreso than normal.  Is the purpose of
> this module to ensure that when the gcache provdider says the write was made
> it was in fact 100% written to the physical disk (or at least accepted by the
> next layer down)?
> 
> Thanks for the info.

The commit message may be of some value to answer the "what" question:

http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/geom/cache/g_cache.c#rev1.1

Regarding the missing manpage, I'd recommand filing a PR (if one
does not already exist).

Regards,

Gary