On Thursday, April 14, 2011 11:26 PM, Benjamin Franz wrote:
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.
Wanna try that again with 64MB of cache only and tell us whether there is a difference in performance?
There is a reason why 3ware 85xx cards were complete rubbish when used for raid5 and which led to the 95xx/96xx series.