On Tue, Jan 12, 2010 at 01:56:57PM -0800, Richard Elling wrote: > On Jan 12, 2010, at 12:37 PM, Gary Mills wrote: > > > On Tue, Jan 12, 2010 at 11:11:36AM -0600, Bob Friesenhahn wrote: > >> On Tue, 12 Jan 2010, Gary Mills wrote: > >>> > >>> Is moving the databases (IMAP metadata) to a separate ZFS filesystem > >>> likely to improve performance? I've heard that this is important, but > >>> I'm not clear why this is. > > > > I found a couple of references that suggest just putting the databases > > on their own ZFS filesystem has a great benefit. One is an e-mail > > message to a mailing list from Vincent Fox at UC Davis. They run a > > similar system to ours at that site. He says: > > > > Particularly the database is important to get it's own filesystem so > > that it's queue/cache are separated. > > Another policy you might consider is the recordsize for the > database vs the message store. In general, databases like the > recordsize to match. Of course, recordsize is a per-dataset > parameter.
Unfortunately, it's not a single database. There are many of them, of different types. One is a Berkeley DB, others are something specific to the IMAP server (called skiplist), and some are small flat files that are just rewritten. All they have in common is activity and frequent locking. They can be relocated as a whole. > > The second one is from: > > > > http://blogs.sun.com/roch/entry/the_dynamics_of_zfs > > > > He says: > > > > For file modification that come with some immediate data integrity > > constraint (O_DSYNC, fsync etc.) ZFS manages a per-filesystem intent > > log or ZIL. > > > > This sounds like the ZIL queue mentioned above. Is I/O for each of > > those handled separately? > > ZIL is for the pool. Yes, I understand that, but do filesystems have separate queues of any sort within the ZIL? If not, would it help to put the database filesystems into a separate zpool? > We did some experiments with the messaging server and a RAID > array with separate logs. As expected, it didn't make much difference > because of the nice, large nonvolatile write cache on the array. This > reinforces the notion that Dan Carosone also recently noted: performance > gains for separate logs are possible when the latency of the separate > log device is much lower than the latency of the devices in the main pool, > and, of course, the workload uses sync writes. It certainly sounds as if latency is the key for synchronous writes. -- -Gary Mills- -Unix Group- -Computer and Network Services- _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
