On 07/18/2011 11:56 PM, Andy wrote:
I'm talking about after I get 2 Intel 320s, should I spend the extra money on a RAID BBU? Adding RAID BBU in this case wouldn't improve reliability, but does it improve performance? If so, how much improvement can it bring?
It won't improve performance enough that I would bother. The main benefit of adding a RAID with BBU to traditional disks is that you can commit much, much faster to the card RAM than the disks can spin. You can go from 100 commits/second to 10,000 commits/second that way (in theory--actually getting >2000 at the database level is harder).
Since the Intel 320 drives can easily hit 2000 to 4000 commits/second on their own, using the cache that's built-in to the drive, the advantage of adding a RAID card on top of that is pretty minimal. Adding a RAID cache will help some, because that layer will be faster than the SSD at absorbing writes, and putting another cache layer into a system always helps with improving burst performance. But you'd probably be better off using the same money to add more RAM, or more/bigger SSD drives. The fundamental thing that RAID BBU units do--speed up commits--you will only see minimal benefit from with these SSDs.
-- Greg Smith 2ndQuadrant US greg@xxxxxxxxxxxxxxx Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
