need help with ZFS

[Pawel Jakub Dawidek]

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 at FreeBSD.org>:
> 
> > > bonnie++ -s17000 -d. -n128
> > > 
> > > for about 10 minutes:
> > > 
> > > http://omploader.org/vMjg5aQ/IMG_0057.jpg  
> > [...]
> > 
> > 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.
> 
> 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.

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