I concur. We did some I/O benchmarking using a 24 drive server, I think it was this server http://supermicro.com/products/chassis/4U/846/SC846E1-R900.cfm with 24 15K SAS drives. The benchmarking was random reads and random writes of varying sizes (multi-gig to make sure it was beyond the total cache available). RAID0 = fastest (just for fun and to set the watermark) RAID10 = second fastest (about 65% of RAID0) RAID5 = a very very distant last (about 20% of RAID0) These % numbers are rough and from memory of several weeks ago. It is combined read and write performance. We also had two 4-gig iram drives in a RAID0, wow that is fast!! _____ From: tclug-list-bounces at mn-linux.org [mailto:tclug-list-bounces at mn-linux.org] On Behalf Of Chris Barber Sent: Wednesday, May 28, 2008 3:58 PM To: tclug-list at mn-linux.org Subject: Re: [tclug-list] OT - Hardware Advice It would be insane to hook up 12 drives in a RAID5. If you lose a drive, it's gonna take a day to rebuild the array and what happens if you lose a second drive while you're rebuilding? 4 x 250GB drives in RAID 5 took about 10 hours to rebuild. It is probably quicker to format and re-install. I hope you have backups. I use RAID 1+0 for database servers. For a app, file, or mail server, I do RAID 1 unless I needed the space, then I'd do RAID 6. I don't run RAID 5 on any of my servers anymore because I need redundancy beyond losing 1 drive and the write performance blows. I should note that you can get sufficient performance from a RAID 5/6 by using a controller with 256MB of cache and allocated most of it to write-back cache. Also, you should have a lot of RAM to cache database pages in RAM and cache queries to avoid hitting the disk. -Chris Bret Baptist wrote: On Wednesday 28 May 2008 1:47:32 pm Josh Paetzel wrote: On Wednesday 28 May 2008 11:14:50 am Justin Krejci wrote: http://download.intel.com/support/motherboards/server/srcsas18e/sb/axxrpc m2 _ tps_10.pdf Benefits are identified in this PDF. Data caching (write-back cache can greatly improve write performance) Busy databases servers commonly need lots of I/O Also consider running RAID10 if you have drive availability (4 drive minimum) as you will get much higher I/O performance with that as well especially with writes. Though if you need the capacity, RAID5 will give you one drive more of capacity. RAID10 can also give you a smaller chance of data loss due to drive failures as you can potentially lose up to half of your drives and still operate whereas using RAID5 and losing 2+ drives = disaster. Somewhere a DBA just rolled over in his grave at the mention of a database using RAID 5. If you're ever going to care about performance at all don't use RAID 5. It's particularly slow at the sorts of write I/O database systems typically generate. For the most part this is true, however on a lot of modern RAID controllers if you hook 12 drives up in RAID-5 you are going to see amazing performance. Here is an article with a very thorough review of 9 SATA RAID cards: http://tweakers.net/reviews/557/26/comparison-of-nine-serial-ata-raid-5-adap ters-pagina-25.html The issue here is that they do not do a RAID-10 test with 12 drives. I don't know what they are doing on the Coraid SR 1521 to make RAID-5 faster than RAID-10, but when you get up to 14 drives in the chassis you get much better throughput, now mind you this is not random I/O, just another thing to think about: http://coraid.com/support/sr/ANSR002.pdf For a large number of drives in a RAID-5 you get really good performance and much higher capacity. Not that this is really relevant to the original poster. Thanks. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mailman.mn-linux.org/pipermail/tclug-list/attachments/20080528/53f1bf28/attachment-0001.htm