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Date:      Sun, 14 Feb 2016 16:40:22 +0800 (AWST)
From:      David Adam <zanchey@ucc.gu.uwa.edu.au>
To:        Tom Curry <thomasrcurry@gmail.com>
Cc:        FreeBSD Filesystems <freebsd-fs@freebsd.org>
Subject:   Re: Poor ZFS+NFSv3 read/write performance and panic
Message-ID:  <alpine.DEB.2.11.1602141625300.1862@motsugo.ucc.gu.uwa.edu.au>
In-Reply-To: <CAGtEZUDCAENGcUjpZDjUBg93F_MWQO40Q4WScm1BogAOUjgEaA@mail.gmail.com>
References:  <alpine.DEB.2.11.1601292153420.26396@motsugo.ucc.gu.uwa.edu.au> <alpine.DEB.2.11.1602080056390.17583@motsugo.ucc.gu.uwa.edu.au> <CAGtEZUDCAENGcUjpZDjUBg93F_MWQO40Q4WScm1BogAOUjgEaA@mail.gmail.com>

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On Mon, 8 Feb 2016, Tom Curry wrote:
> On Sun, Feb 7, 2016 at 11:58 AM, David Adam <zanchey@ucc.gu.uwa.edu.au>
> wrote:
> 
> > Just wondering if anyone has any idea how to identify which devices are
> > implicated in ZFS' vdev_deadman(). I have updated the firmware on the
> > mps(4) card that has our disks attached but that hasn't helped.
> 
> I too ran into this problem and spent quite some time troubleshooting
> hardware. For me it turns out it was not hardware at all, but software.
> Specifically the ZFS ARC. Looking at your stack I see some arc reclaim up
> top, it's possible you're running into the same issue. There is a monster
> of a PR that details this here
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=187594
> 
> If you would like to test this theory out, the fastest way is to limit the
> ARC by adding the following to /boot/loader.conf and rebooting
> vfs.zfs.arc_max="24G"
> 
> Replacing 24G with what makes sense for your system, aim for 3/4 of total
> memory for starters. If this solves the problem there are more scientific
> methods to a permanent fix, one would be applying the patch in the PR
> above, another would be a more finely tuned arc_max value.

Thanks Tom - this certainly did sound promising, but setting the ARC to 
11G of our 16G of RAM didn't help. `zfs-stats` confirmed that the ARC was 
the expected size and that there was still 461 MB of RAM free.

We'll keep looking!

David Adam
zanchey@ucc.gu.uwa.edu.au



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