Next Steps to Debug ZFS Hang?

[Valeri Galtsev]

On Thu, October 9, 2014 5:53 pm, Daniel Staal wrote:
> --As of October 8, 2014 9:28:05 PM -0700, Nick Sivo is alleged to have
> said:
>
>>> Not sure if this will be helpful, but at least it shouldn't hurt:  When
>>> was the last time you ran a scrub?  Also, how much RAM do you have and
>>> where is your swap?  (The only times I've had permanent hangs from ZFS
>>> was when I ran out of RAM and was trying to swap to ZFS...)
>>
>> The server has 64GB ECC RAM, and no swap at the moment. I've since
>> rebooted the box, but a scrub today revealed no errors, and there was
>> nothing in the console or any log files about disk or controller
>> errors or timeouts.
>
> --As for the rest, it is mine.
>
> Note that I'm still just going by 'standard checks', but why don't you
> have
> any swap?  I know you probably wouldn't use it with that much RAM around,
> but FreeBSD still performs better with it - and it wouldn't surprise me
> completely if that was causing your issue.

I'm petrified. Is that so? I mean, as I understood you, 64 GB RAM machine
running under FreeBSD (say, 9.3) still needs some amount of SWAP for
better performance, right?

Valeri

> (It shouldn't, in an ideal
> world - but it's an oddity on your system that might be causing issues, if
> there's an uncovered corner case.)
>
> Setting up a small ramdisk for swap - or even putting some small
> swap-on-zfs - might be worth checking to see if it seems to prevent the
> issue.  (Note that swap-on-zfs has a 'worst case' scenario that crashes
> the
> box if you run out of RAM.  It's happened to me, and I was able to
> recover,
> but it took a while.)
>
> Anyway, I'm mostly trying to keep your question alive in hopes that
> someone
> who's more knowledgeable can answer it.  ;)
>
> Daniel T. Staal
>
> ---------------------------------------------------------------
> This email copyright the author.  Unless otherwise noted, you
> are expressly allowed to retransmit, quote, or otherwise use
> the contents for non-commercial purposes.  This copyright will
> expire 5 years after the author's death, or in 30 years,
> whichever is longer, unless such a period is in excess of
> local copyright law.
> ---------------------------------------------------------------
> _______________________________________________
> freebsd-questions at freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-questions
> To unsubscribe, send any mail to
> "freebsd-questions-unsubscribe at freebsd.org"
>


++++++++++++++++++++++++++++++++++++++++
Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247
++++++++++++++++++++++++++++++++++++++++