On 08/24/2011 01:23 PM, Andy wrote:
Many SSDs that claim better are cheating though, or only quoting under conditions that don't take into account drive cleanup operations. That's fine in a non-database context, but if the data isn't any good to you unless it's guaranteed to be safe either on disk or on a non-volatile cache, Intel's numbers are the more relevant ones. I wouldn't assume other drives really are better unless it's in a true apples to apples fair comparison. I published some numbers at http://archives.postgresql.org/message-id/4D9D1FC3.4020207@xxxxxxxxxxxxxxx that suggested 400 TPS was the worst-case for this drive on database random writes running the pgbench workload, which does a couple of writes per commit. That's only 2X as fast as a typical mechanical hard drive running the same workload. On random reads, the performance gap is much bigger, in favor of the SSD. I've measured the performance of this drive from a couple of directions now, and it always comes out the same. For PostgreSQL, reading or writing 8K blocks, I'm seeing completely random workloads hit a worst-case of 20MB/s; that's just over 2500 IOPS. It's quite possible that number can go lower under pressure of things like internal drive garbage collection however, which I believe is going into the 600 IOPS figure. I haven't tried to force that yet--drive is too useful to me to try and burn it out doing tests like that at the moment. -- Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD PostgreSQL Training, Services, and 24x7 Support www.2ndQuadrant.us |
