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: http://blogs.digitar.com/jjww/?itemid=52 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. -Michael --On Wednesday, November 14, 2007 8:15 PM -0800 Vincent Fox <vbfox@xxxxxxxxxxx> 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 > mailboxes.db > or deliver.db start getting stacked up, due to the favoritism shown to > reads? > 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 > slowdown. > > 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 ---- 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
