> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss- > boun...@opensolaris.org] On Behalf Of Andreas Höschler > > I would like to remove the two SSDs as log devices from the pool and > instead add them as a separate pool for sole use by the database to > see how this enhences performance. I could certainly do > > zpool detach tank c1t7d0 > > to remove one disk from the log mirror. But how can I get back the > second SSD?
If you're running solaris, sorry, you can't remove the log device. You better keep your log mirrored until you can plan for destroying and recreating the pool. Actually, in your example, you don't have a mirror of logs. You have two separate logs. This is fine for opensolaris (zpool >=19), but not solaris (presently up to zpool 15). If this is solaris, and *either* one of those SSD's fails, then you lose your pool. If you're running opensolaris, "man zpool" and look for "zpool remove" Is the database running locally on the machine? Or at the other end of something like nfs? You should have better performance using your present config than just about any other config ... By enabling the log devices, such as you've done, you're dedicating the SSD's for sync writes. And that's what the database is probably doing. This config should be *better* than dedicating the SSD's as their own pool. Because with the dedicated log device on a stripe of mirrors, you're allowing the spindle disks to do what they're good at (sequential blocks) and allowing the SSD's to do what they're good at (low latency IOPS). If you're running zpool 19 or greater (you can check with "zpool update") it should be safe to run with the log device un-mirrored. In which case, you might think about using one SSD as log, and one SSD as cache. That might help. You can verify the behavior of your database, if you run "zpool iostat" and then do some database stuff, you should see the writes increasing on the log SSD's. If you don't see that, then your DB is not doing sync writes (I bet it is). You don't benefit from dedicated log device unless you're doing sync writes. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
