LARGE single-system Cyrus installs?
baconm at email.unc.edu
Thu Nov 15 10:04:34 EST 2007
Interesting thought. We haven't gone to ZFS yet, although I like the idea
a lot. My hunch is it's an enormous win for the mailbox partitions, but
perhaps it's not a good thing for the meta partition. I'll have to let
someone else who knows more about ZFS and write speeds vs. read speeds
chime in here.
I have heard tell of funny behavior that ZFS does if you've got
battery-backed write caches on your arrays. (i.e., ZFS aggressively
flushes those caches, making them essentially useless.) Here's the best
article I was able to find on it in a short google:
Only do that, of course, if you can trust your drives to write the data in
the caches in case of a power outage, and if you don't have any non-battery
backed caches somewhere else on your system.
--On Wednesday, November 14, 2007 8:15 PM -0800 Vincent Fox
<vbfox at ucdavis.edu> wrote:
> This thought has occurred to me:
> ZFS prefers reads over writes in it's scheduling.
> I think you can see where I'm going with this. My WAG is something
> related to Pascal's, namely latency. What if my write requests to
> or deliver.db start getting stacked up, due to the favoritism shown to
> The actual usage mix on a Cyrus system ends up being more writes than
> reads. Despite having channels that seem under-utilized perhaps the
> stacking of small latencies hits a tipping point that is causing the
> We have all Cyrus lumped in one ZFS pool, with separate filesystems for
> imap, mail, sieve, etc. However, I do have an unused disk in each array
> such that I could setup a simple ZFS mirror pair for /var/cyrus/imap so
> that the databases are in their own pools. Or even I suppose a UFS
> filesystem with directio and all that jazz set. Perhaps I wouldn't get
> all the
> effects of a RAM-SAN 500 but it could be a worthwhile improvement.
> I liked having one big pool, but if it works, c'est la vie.
> Cyrus Home Page: http://cyrusimap.web.cmu.edu/
> Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki
> List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
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