On 19.2.2014 19:09, Scott Marlowe wrote: > > You can also do the old trick of underprovisioning and / or > underutilizing all the space on SSDs. I.e. put 10 600GB SSDs under a > HW RAID controller in RAID-10, then only parititon out 1/2 the storage > you get from that. so you get 1.5TB os storage and the drives are > underutilized enough to have spare space. Yeah. AFAIK that's basically what Intel did with S3500 -> S3700. What I'm trying to find is the 'sweet spot' considering lifespan, capacity, performance and price. That's why I'm still wondering if there are some experiences with current generation of SSDs and RAID controllers, with RAID levels other than RAID-10. Say I have 8x 400GB SSD, 75k/32k read/write IOPS each (i.e. it's basically the S3700 from Intel). Assuming the writes are ~25% of the workload, this is what I get for RAID10 vs. RAID6 (math done using http://www.wmarow.com/strcalc/) | capacity GB | bandwidth MB/s | IOPS --------------------------------------------------- RAID-10 | 1490 | 2370 | 300k RAID-6 | 2230 | 1070 | 130k Let's say the app can't really generate 130k IOPS (we'll saturate CPU way before that), so even if the real-world numbers will be less than 50% of this, we're not going to hit disks as the main bottleneck. So let's assume there's no observable performance difference between RAID10 and RAID6 in our case. But we could put 1.5x the amount of data on the RAID6, making it much cheaper (we're talking about non-trivial numbers of such machines). The question is - how long will it last before the SSDs die because of wearout? Will the RAID controller make it worse due to (not) handling TRIM? Will we know how much time we have left, i.e. will the controller provide the info the drives provide through SMART? > Right now I'm testing on a machine with 2x Intel E5-2690s > (http://ark.intel.com/products/64596/intel-xeon-processor-e5-2690-20m-cache-2_90-ghz-8_00-gts-intel-qpi) > 512GB RAM and 6x600GB Intel SSDs (not sure which ones) under a LSI Most likely S3500. S3700 are not offered with 600GB capacity. > MegaRAID 9266. I'm able to crank out 6500 to 7200 TPS under pgbench on > a scale 1000 db at 8 to 60 clients on that machine. It's not cheap, > but storage wise it's WAY cheaper than most SANS and very fast. > pg_xlog is on a pair of non-descript SATA spinners btw. Nice. I've done some testing with fusionio iodrive duo (2 devices in RAID0) ~ year ago, and I got 12k TPS (or ~15k with WAL on SAS RAID). So considering the price, the 7.2k TPS is really good IMHO. regards Tomas -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
