ZFS question

Reed A. Cartwright cartwright at asu.edu
Thu Mar 21 05:10:22 UTC 2013

Note that my issue seems to do with an interaction between the CAM
system and the MPS driver in 9.1.  Thus it is more than likely
different than what you are experiencing Quartz.

Now that ZFS deadman has been incorporated into stable, I'll probably
give a 9.1 (i.e. 9/stable) another try.

Jeremy, I have a question about enabling kernel dumps based on my
current swap config.

I currently have a 1TB drive split into 4 geli encrypted swap
partitions (Freebsd doesn't like swap partitions over ~250 GB and I
have lots of RAM).  These partitions are UFS-swap partitions and are
not backed by any mirroing or ZFSing.

So, how do I best enable crash dumps?  If I need to remove encryption,
I can do that.

On Wed, Mar 20, 2013 at 9:45 PM, Jeremy Chadwick <jdc at koitsu.org> wrote:
> (Please keep me CC'd as I'm not subscribed to -questions)
> Lots to say about this.
> 1. freebsd-fs is the proper list for filesystem-oriented questions of
> this sort, especially for ZFS.
> 2. The issue you've described is experienced by some, and **not**
> experienced by even more/just as many, so please keep that in mind.
> Each/every person's situation/environment/issue has to be treated
> separately/as unique.
> 3. You haven't provided any useful details, even in your follow-up post
> here:
> http://lists.freebsd.org/pipermail/freebsd-questions/2013-March/249958.html
> All you've provided is a "general overview" with no technical details,
> no actual data.  You need to provide that data verbatim.  You need to
> provide:
> - Contents of /boot/loader.conf
> - Contents of /etc/sysctl.conf
> - Output from "zpool status"
> - Output from "zpool get all"
> - Output from "zfs get all"
> - Output from "dmesg" (probably the most important)
> - Output from "sysctl vfs.zfs kstat.zfs"
> I particularly tend to assist with disk-level problems, so if this turns
> out to be a disk-level issue (and NOT a controller or controller driver
> issue), I can help quite a bit with that.
> 4. I would **not** suggest rolling back to 9.0.  This recommendation is
> solves nothing -- if there is truly a bug/livelock issue, then that
> needs to be tracked down.  By rolling back, if there is an issue, you're
> effectively ensuring it'll never get investigated or fixed, which means
> you can probably expect to see this in 9.2, 9.3, or even 10.x onward.
> If you can't deal with the instability, or don't have the
> time/cycles/interest to help track it down, that's perfectly okay too:
> my recommendation is to go back to UFS (there's no shame in that).
> Else, as always, I strongly recommend running stable/9 (keep reading).
> 5. stable/9 (a.k.a. FreeBSD 9.1-STABLE) just recently (~5 days ago)
> MFC'd an Illumos ZFS feature solely to help debug/troubleshoot this
> exact type of situation: introduction of the ZFS deadmean thread.
> Reference materials for what that is:
> http://svnweb.freebsd.org/base?view=revision&revision=248369
> http://svnweb.freebsd.org/base?view=revision&revision=247265
> https://www.illumos.org/issues/3246
> The purpose of this feature (enabled by default) is to induce a kernel
> panic when ZFS I/O stalls/hangs for unexpectedly long periods of time
> (configurable via vfs.zfs.deadman_synctime).
> Once the panic happens (assuming your system is configured with a slice
> dedicated to swap (ZFS-backed swap = bad bad bad) and use of
> dumpdev="auto" in rc.conf), upon reboot the system should extract the
> crash dump from swap and save it into /var/crash.  At that point kernel
> developers on the -fs list can help tell you *exactly* what to do with
> kgdb(1) that can shed some light on what happened/where the issue may
> lie.
> All that's assuming that the issue truly is ZFS waiting for I/O and not
> something else (like ZFS internally spinning hard in its own code).
> Good luck, and let us know how you want to proceed.
> --
> | Jeremy Chadwick                                   jdc at koitsu.org |
> | UNIX Systems Administrator                http://jdc.koitsu.org/ |
> | Mountain View, CA, US                                            |
> | Making life hard for others since 1977.             PGP 4BD6C0CB |
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Reed A. Cartwright, PhD
Assistant Professor of Genomics, Evolution, and Bioinformatics
School of Life Sciences
Center for Evolutionary Medicine and Informatics
The Biodesign Institute
Arizona State University

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