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Date:      Wed, 9 Sep 2009 12:43:58 +0200
From:      Pawel Jakub Dawidek <pjd@FreeBSD.org>
To:        Danny Carroll <fbsd@dannysplace.net>
Cc:        freebsd-fs@freebsd.org, freebsd-stable@freebsd.org
Subject:   Re: zfs kernel panic
Message-ID:  <20090909104358.GG1901@garage.freebsd.pl>
In-Reply-To: <4AA77834.1010007@dannysplace.net>
References:  <20090908172332.476d9e0b.gerrit@pmp.uni-hannover.de> <20090908164413.GC1539@garage.freebsd.pl> <20090909090715.9d8a58ef.gerrit@pmp.uni-hannover.de> <20090909083313.GA1901@garage.freebsd.pl> <4AA77834.1010007@dannysplace.net>

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On Wed, Sep 09, 2009 at 07:41:08PM +1000, Danny Carroll wrote:
> On 9/09/2009 6:33 PM, Pawel Jakub Dawidek wrote:
> >On Wed, Sep 09, 2009 at 09:07:15AM +0200, Gerrit K=FChn wrote:
> >  =20
> >>On Tue, 8 Sep 2009 18:44:13 +0200 Pawel Jakub Dawidek<pjd@FreeBSD.org>
> >>wrote about Re: zfs kernel panic:
> >>
> >>PJD>  If this is amd64, add vm.kmem_size=3D"4G" to your loader.conf bac=
k.
> >>
> >>What about vm.kmem_size_max? Does that also need tuning?
> >>    =20
> >No, this should be auto-tuned to some very large value.
> >
> >  =20
> Pawel (et al),
>=20
> Would it be possible for you to post to the list your ideas of a=20
> complete set of tuning parameters for ZFS on amd64?  I have used the=20
> wiki article as a reference (http://wiki.freebsd.org/ZFSTuningGuide) but=
=20
> it states that if you have > 2g ram and 7.2 then you do not need to tune=
=20
> at all.

I think that was the idea, although I see no reason to have less kernel
address space than physical memory (except there might be other
in-kernel variables auto-tuned based on kmem size).

> I for one would be interested in learning a little more about how the=20
> memory should be tuned.  Specifically what might be interesting is to=20
> know, once a parameter is set, is there an easy way to find out how it's=
=20
> being used? i.e. If you start limiting the arc, is is possible to know=20
> what sort of hit/miss rate you are getting.

There are ARC statistics available here:

	# sysctl kstat.zfs

--=20
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd@FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!

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