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.
There isn't a patch for this one yet, but Sun will supply an IDR if
you open a support case.
--
-Gary Mills- -Unix Support- -U of M Academic Computing and Networking-
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