current zfs tuning in RELENG_7 (AMD64) suggestions ?

[Alan Cox]

On Fri, May 1, 2009 at 6:28 PM, Freddie Cash <fjwcash at gmail.com> wrote:

> On Fri, May 1, 2009 at 4:12 PM, Louis Kowolowski
> <louisk at cryptomonkeys.org> wrote:
> > On May 1, 2009, at 1:53 PM, Pete French wrote:
> >> ...
> >> The tuning isn't there to improve performance, it's there to prevent
> >> the box going titus due to a panic when the ARC gets too big, and
> >> you are missing the mian one, which is to limit the size of the ARC.
> >> On recent versions of BSD (and you are running 7.2, so thats fine) then
> >> the defaults for kmem size are fine, but you still need something like
> >> this:
> >>
> >> vfs.zfs.arc_max="256M"
> >>
> >> In there to stop the ARC growing. thats the only tuning I have on
> >> my 4 gig machine, which takes a steady stream of data and is used
> >> for taking backup snapshots. ZFS is excellent, and for me is perfectly
> >> stable, to the point where I am starting to roll it out to production
> >> machines, with the above tuning.
> >>
> > I agree, although I'm using 384 instead of 256.  My systems have been
> > running in production for almost a year now w/o any ZFS issues.
>
> The exact value to use will depend on the system.  Particularly on the
> amount of RAM in the system, and what kmem_max is set to.  A
> "rule-of-thumb" we've been using is:
>   kmem_max should be half of the amount of RAM (or 1.5 GB as that's
> the current max)


This information is outdated.  The current max in RELENG_7 for amd64 is
~3.75GB.

Regards,
Alan