System freezes up during long-running ZFS disk activity

Christian Campbell dcamp at
Wed Feb 19 20:07:36 UTC 2014

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

* 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,

3425 SW 2nd Ave, #239                              cell (352) 514-7411
Gainesville, FL  32607-2813                   dcamp at

On this perfect day / Nothing's standing in my way...        -Hoku

More information about the freebsd-questions mailing list