Gary Mills writes:
> 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? > The slog device is for the pool but the ZIL is per filesystem/dataset. The logbias property can be used on a dataset to prevent that set from consuming the slog device resource : http://blogs.sun.com/roch/entry/synchronous_write_bias_property -r > > 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 _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
