On 04/14/2011 08:04 AM, Christopher Chan wrote: > >> Then try both for your use case and your hardware. We have wide raid6 setups >> that does well over 500 MB/s write (that is: not all raid6 writes suck...). >> > /me replaces all of Peter's cache with 64MB modules. > > Let's try again. If you are trying to imply that RAID6 can't go fast when write size is larger than the cache, you are simply wrong. Even with just a 8 x RAID6, I've tested a system as sustained sequential (not burst) 156Mbytes/s out and 387 Mbytes/s in using 7200 rpm 1.5 TB drives. Bonnie++ results attached. Bonnie++ by default uses twice as much data as your available RAM to make sure you aren't just seeing cache. IOW: That machine only had 4GB of RAM and 256 MB of controller cache during the test but wrote and read 8 GB of data for the tests. Version 1.96 ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP xxxx 8G 248 99 155996 74 85600 42 961 99 386900 62 628.3 29 Latency 33323us 224ms 1105ms 19047us 77599us 113ms Version 1.96 ------Sequential Create------ --------Random Create-------- xxxx -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP 16 17395 56 +++++ +++ 23951 61 27125 84 +++++ +++ 32154 84 Latency 330us 993us 980us 344us 64us 80us -- Benjamin Franz