On Mon, Apr 05, 2010 at 07:43:26AM -0400, Edward Ned Harvey wrote: > 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).
Others have addressed the rest of the issues well enough, but I thought I'd respond on this point. What you say is fair, if the db is bound by sync write latency. If it is bound by read latency, you will still suffer. You could add more ssd's as l2arc (and incur more memory overhead), or you could put the whole pool on ssd (and lose its benefit for other pool uses). There are many factors here that will determine the best config, but the current one may well not be the optimal. -- Dan.
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