On Tue, Feb 10, 2009 at 11:55 PM, John R Pierce <pierce@xxxxxxxxxxxx> wrote: > Sebastian Böhm wrote: >> >> I consider buying one of these Intel SSDs for my Database (MLC). >> ..... >> currently I have a lot of small random reads/writes causing heavy iowait. > > how many r/s and w/s in `iostat -x 5` while your database is humming are you > seeing now? Thats the single key performance factor in disk bound > database IO. Caches can reduce the r/s requirements but the writes have to > go to disk if you want data integrity. ok, a raid controller with battery > back cache configured for writeback can accelerate the writes by a lot too. > > a desktop 7200 rpm SATA drive will saturate at under 100 IO ops/sec max with > the typical 8kbyte random blocks of a database, while a 15k server drive can > sustain 200 io/sec, and a raid 1+0 can hit several times more (I've seen > sustained 200/s on each of 4 15k spindles) while still using normal hard > disks. Those intel SSDs are supposed to be good for 1000 or so IOP/sec if > I remember correctly... (of course, in a mirror, you have to half the > aggregated writes for the true number of useful random writes) Also keep in mind that a fast battery backed caching RAID controller can get several thousand transactions per second on a large number of spindles by re-ordering writes and such. I can get anywhere from 1800 to 3400 tps on 12 15k disks in RAID-10 (i.e. 6 disk RAID-0 performance) and that's sustained over a very long test, usually 30 minutes to a few hours with pgbench. The size of the test set and server config parameters make for the variations from 1800 to 3400. I think the real advantage to the SSDs is that they can get this kind of performance, or even more from a rather small software RAID-10 of 4 disks. Instead of spending $800 on a RAID controller, use it towards buying more SSDs. As the price of SSDs falls much faster than the cost of high end RAID controllers, they'll reach a point where any old 4x2.5" server can walk right into your data center and take over the job of a much larger $10,000+ server. I'd really like to see how 16 or more of them in a big RAID-10 both on a RAID controller and maybe in jbod mode ran. Anyone at some big corporation got some time to benchmark the next great thing? I'd take a day off just to come watch that. -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
