On Mon, Apr 27, 2009 at 04:47:27PM -0500, Gary Mills wrote:
> On Sat, Apr 18, 2009 at 04:27:55PM -0500, Gary Mills wrote:
> > We have an IMAP server with ZFS for mailbox storage that has recently
> > become extremely slow on most weekday mornings and afternoons. When
> > one of these incidents happens, the number of processes increases, the
> > load average increases, but ZFS I/O bandwidth decreases. Users notice
> > very slow response to IMAP requests. On the server, even `ps' becomes
> > slow.
>
> The cause turned out to be this ZFS bug:
>
> 6596237: Stop looking and start ganging
>
> Apparently, the ZFS code was searching the free list looking for the
> perfect fit for each write. With a fragmented pool, this search took
> a very long time, delaying the write. Eventually, the requests arrived
> faster than writes could be sent to the devices, causing the server
> to be unresponsive.
We also had another problem, due to this ZFS bug:
6591646: Hang while trying to enter a txg while holding a txg open
This was a deadlock, with one thread blocking hundreds of other
threads. Our symptom was that all zpool I/O would stop and the `ps'
command would hang. A reboot was the only way out.
If you have a support contract, Sun will supply an IDR that fixes
both problems.
--
-Gary Mills- -Unix Support- -U of M Academic Computing and Networking-
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