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Date:      Mon, 31 Aug 2009 13:08:08 +0200
From:      Pawel Jakub Dawidek <pjd@FreeBSD.org>
To:        Kai Gallasch <gallasch@free.de>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: need help with ZFS
Message-ID:  <20090831110808.GF1671@garage.freebsd.pl>
In-Reply-To: <20090830191336.5f1cdec0@orwell.free.de>
References:  <4A927CB3.3040402@plus-plus.su> <4A964F4E.4080009@plus-plus.su> <4A9656CE.8020107@plus-plus.su> <367b2c980908270316n7a21673ek3a997573f2fadbb0@mail.gmail.com> <4A96731D.20406@plus-plus.su> <4A967680.2030205@plus-plus.su> <4A969D20.40809@plus-plus.su> <20090829160037.GA1848@garage.freebsd.pl> <20090830191336.5f1cdec0@orwell.free.de>

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On Sun, Aug 30, 2009 at 07:13:36PM +0200, Kai Gallasch wrote:
> On Sat, 29 Aug 2009 18:00:37 +0200
> wrote Pawel Jakub Dawidek <pjd@FreeBSD.org>:
>=20
> > > bonnie++ -s17000 -d. -n128
> > >=20
> > > for about 10 minutes:
> > >=20
> > > http://omploader.org/vMjg5aQ/IMG_0057.jpg =20
> > [...]
> >=20
> > I'm running your test on pretty low-end h/w (i386, 1GB of RAM, two
> > cores) and cannot reproduce the problem for few hours now. The only
> > tuning I did was to set vm.kmem_size to 1GB. You still need to do
> > this very tuning even on amd64.
>=20
> Hi.
> Could you give a short explanation why on amd64 it is still necessary
> to set vm.kmem_size to 1GB ? I thought with zfs on FreeBSD-7.2-STABLE
> tuning kmem was not necessary any more.

Actually I might be wrong. I was sure I saw amd64 machine with low
vm.kmem_size, but I checked on 8GB RAM machine and it is auto-tuned to
more than 2.5GB. I still prefer to set it to 8GB just in case and
eventually limit ARC size.

> The reason I ask is, I have some servers on FreeBSD-7.2-STABLE
> AMD64 that are quite stable, but sometimes suffer from zfs
> performance degradation when zfs is competing with applications using
> huge amounts of RAM. Those servers are not swapping at all when this
> takes place.

--=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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