current zfs tuning in RELENG_7 (AMD64) suggestions ?

[Freddie Cash]

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)
   arc_max should be half of kmem_max

Using those, we've been able to run our ZFS boxes without any kmem
panics, even when doing rsync backups for 102 remote servers every
night to a single box.

Finding those values was fun.  :(
-- 
Freddie Cash
fjwcash at gmail.com