----- Original Message -----
From: "Jeremy Chadwick" <j...@koitsu.org>
To: "Ben Morrow" <b...@morrow.me.uk>
Cc: <freebsd-stable@freebsd.org>
Sent: Tuesday, March 05, 2013 5:32 AM
Subject: Re: ZFS "stalls" -- and maybe we should be talking about defaults?
On Tue, Mar 05, 2013 at 05:05:47AM +0000, Ben Morrow wrote:
Quoth Karl Denninger <k...@denninger.net>:
>
> Note that the machine is not booting from ZFS -- it is booting from and
> has its swap on a UFS 2-drive mirror (handled by the disk adapter; looks
> like a single "da0" drive to the OS) and that drive stalls as well when
> it freezes. It's definitely a kernel thing when it happens as the OS
> would otherwise not have locked (just I/O to the user partitions) -- but
> it does.
Is it still the case that mixing UFS and ZFS can cause problems, or were
they all fixed? I remember a while ago (before the arc usage monitoring
code was added) there were a number of reports of serious probles
running an rsync from UFS to ZFS.
This problem still exists on stable/9. The behaviour manifests itself
as fairly bad performance (I cannot remember if stalling or if just
throughput rates were awful). I can only speculate as to what the root
cause is, but my guess is that it has something to do with the two
caching systems (UFS vs. ZFS ARC) fighting over large sums of memory.
In our case we have no UFS, so this isn't the cause of the stalls.
Spec here is
* 64GB RAM
* LSI 2008
* 8.3-RELEASE
* Pure ZFS
* Trigger MySQL doing a DB import, nothing else running.
* 4K disk alignment
Regards
Steve
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