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. >> >> There is an obvious potential benefit in that you are then able to >> tune filesystem parameters to best fit the needs of the application >> which updates the data. For example, if the database uses a small >> block size, then you can set the filesystem blocksize to match. If >> the database uses memory mapped files, then using a filesystem >> blocksize which is closest to the MMU page size may improve >> performance. > > 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. > 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. 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. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
