Yeb Havinga wrote:
Probably like many other's I've wondered why no SSD manufacturer puts a small BBU on a SSD drive. Triggered by Greg Smith's mail http://archives.postgresql.org/pgsql-performance/2010-02/msg00291.php here, and also anandtech's review at http://www.anandtech.com/show/2899/1 (see page 6 for pictures of the capacitor) I ordered a SandForce drive and this week it finally arrived.
Note that not all of the Sandforce drives include a capacitor; I hope you got one that does! I wasn't aware any of the SF drives with a capacitor on them were even shipping yet, all of the ones I'd seen were the chipset that doesn't include one still. Haven't checked in a few weeks though.
* How to test for power failure?
I've had good results using one of the early programs used to investigate this class of problems: http://brad.livejournal.com/2116715.html?page=2
You really need a second "witness" server to do this sort of thing reliably, which that provides.
* What filesystem to use on the SSD? To minimize writes and maximize chance for seeing errors I'd choose ext2 here.
I don't consider there to be any reason to deploy any part of a PostgreSQL database on ext2. The potential for downtime if the fsck doesn't happen automatically far outweighs the minimal performance advantage you'll actually see in real applications. All of the benchmarks showing large gains for ext2 over ext3 I have seen been synthetic, not real database performance; the internal ones I've run using things like pgbench do not show a significant improvement. (Yes, I'm already working on finding time to publicly release those findings)
Put it on ext3, toggle on noatime, and move on to testing. The overhead of the metadata writes is the least of the problems when doing write-heavy stuff on Linux.
-- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support greg@xxxxxxxxxxxxxxx www.2ndQuadrant.us -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
