[zfs-discuss] ZFS configuration/tuning for laptop?

Marko Schütz Schmuck MarkoSchuetz at web.de
Thu Oct 3 10:53:45 EDT 2013

At Tue, 01 Oct 2013 12:14:29 -0700,
Bryn Hughes wrote:
> On 13-10-01 12:03 PM, Marko Schütz Schmuck wrote:
> > Dear All,
> >
> > I am running Ubuntu 12.10, kernel 3.5.0-41 on a laptop with a Seagate
> > Momentus 7200.4 500GB hard disk and 8GB RAM.
> >
> > Sometimes I am seeing _very_ high load averages (>240) with constant
> > disk activity. I am not sure whether these are related to ZFS, but
> > maybe they are... Maybe someone has seen something like this before...
> >
> > The laptop has a small ext4 disk and one zpool. It swaps to a zvol on
> > that pool.
> >
> > I had suspected that ARC is competing with other loads and had fixed
> > zfs_arc_min and zfs_arc_max both at !GB. But that has not helped.
> >
> > So any specific ideas on this problem and/or general advise on ZFS +
> > laptop configuration/tuning would be greatly appreciated.
> >
> > Best regards
> >
> > Marko
> Load averages that high are almost always related to a dramatic shortage
> of memory. 
> I see you have swap on a zvol - that may be the source of your issues. 
> Make sure you have primarycache=none set for your swap zvol as there's
> no sense trying to use memory to cache what you are swapping.  If you
> haven't done this already that is likely a decent portion of your problem.
> Note also I believe I have seen issues mentioned on here when
> zfs_arc_min and zfs_arc_max are set to the same values.  I'd suggest not
> doing that. 
> Finally you can see what your actual arc memory usage is by looking at
> /proc/spl/kstat/zfs/arcstats - look at 'c' and 'size' to see what you
> are actually at with your ARC.

Yes. I kept that running for a few weeks, but saw nothing suspicious

Thank you very much for the suggestions. I did not have
primarycache=none set on swap (fixed now), but the machine wasn't
swapping at all when it happened.

It seems I was barking up the wrong tree: I suspect that a defect in
byobu+tmux that kept forking processes was responsible for the very
high load averages. I have switched to byobu+screen and will see
whether the high loads happen again.

Best regards,

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