System freezes up during long-running ZFS disk activity

Dennis Glatting dg at
Wed Feb 19 20:22:30 UTC 2014

Sorry, I forgot to mention this URL:

On Wed, 2014-02-19 at 15:06 -0500, Christian Campbell wrote:
> I recently installed 9.2-RELEASE-p3 on a Dell Precision T5400. I'm using
> ZFS filesystem version: 5, ZFS storage pool version: features support
> (5000). The pool was imported from a previous 9.2 box on which it worked
> without issue.
> I don't know if my problem is ZFS-related, but my ZFS use is why I noticed
> it and I seem to be able to reproduce it reliably. Every so often, from
> minutes to hours, my computer will freeze up while ZFS has been busy. This
> happens during a resilver, a scrub, and a long-running process reading
> millions of files from the pool. When it freezes, all output and input
> freezes: tasks like zpool iostat -v 1 or top stop updating their output,
> whether on the console or an ssh terminal over Ethernet. Pressing keys does
> not garner a response.* Sometimes a freeze lasts minutes and then proceeds
> on its own. Sometimes it goes on for hours. An action that typically, but
> not always, jogs it is unplugging the USB keyboard -- the disk activity
> resumes immediately, and any queued keyboard input immediately plays out
> whether on the console or over ssh. Lastly, my ssh terminal (PuTTY) will
> stay connected for hours during a freeze-up, *i.e.* the TCP circuit is not
> closed or timed out, as opposed to closing pretty quickly after the server
> is powered off.
> In all cases, the system clock lags by the sum of the durations of the
> freezes.
> * During an initial resilver, I noticed that pressing a key such as Ctrl on
> the USB keyboard would jog it, but pressing Ctrl or other keys doesn't jog
> my process of long-running IO activity. But in all cases, even when
> unplugging and replugging the USB keyboard doesn't jog it, Ctrl-Alt-Del
> prompts an orderly shutdown.
> Debugging advise is very welcome!
> Thank you,
> Christian
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Dennis Glatting <dg at>

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