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