On Tue 03 May 2011 at 05:20:52 -0700, Jeremy Chadwick wrote:
> To be on the safe side, pick something that's small at first, then work
> your way up.  You'll need probably 1+ weeks of heavy ZFS I/O between
> tests (e.g. don't change the tunable, reboot, then 4 hours later declare
> the new (larger) value as stable).

Ah, that's important: so far it seemed to me that a *too small* value
(for all various tunables) would cause problems, but now you're saying
that *too large* is the problem (at least for vfs.zfs.arc_max)! 

This machine has mixed loads; from time to time somebody starts a big
job with lots of I/O, and in between it is much more modestly loaded.

> So for example on an 8GB RAM machine, I might recommend starting with
> vfs.zfs.arc_max="4096M" and let that run for a while.  If you find your
> "Wired" value in top(1) remains fairly constant after a week or so of
> heavy I/O, consider bumping up the value a bit more (say 4608M).

I'll do just that.

> Sorry to make this long-winded; bad habit of mine that I've never
> managed to break.

Oh no problem, it turns out to be eye-opening!

> | Jeremy Chadwick                                   j...@parodius.com |
-Olaf.
-- 
Pipe rene = new PipePicture(); assert(Not rene.GetType().Equals(Pipe));
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