Hey! Not a question, actually, but I'm posting it for (hopefully) someones benefit. There are many questions on this topic up here, and a lot of conflicting info.
When looking to replace our DB server with a new one, I wanted to find the "best" RAID solution. I initially thought I'd go with RAID 10 (striped sets, mirrored). I purchased the Adaptec 5805 RAID controller, bought 5 Seagate 72GB Cheetah SAS drives, and put them all in a fast new server. The Adaptec documentation mentioned RAID 5EE (striping, with parity, so if any one disk fails you're OK). The documentation indicated that 5EE had the best read times, but slowest write times of the various RAID options. Since most of our bottlenecks seem to be reading from the DB I decided to go that route instead.
Bad decision! I have done a lot of testing, and here is what I have come up with. All these times are for copying a 2.2GB file from one location to another locally.
Copy from RAID 5EE to single SATA-II drive: 27 seconds
Copy from single SATA-II drive to RAID 5EE array: 260 seconds
That's not a typo... it took 9 1/2 times as long to write to the RAID 5EE !
So I reconfigured the system to RAID 10 (4 disks) plus a hot spare. New times:
Copy from RAID 10 to single SATA-II drive: 29 seonds
Copy from single SATA-II drive to RAID 10 array: 34 seconds.
(BTW... I repeated these tests with larger files and got comparable results)
I am **more** than happy to lose a minimal amount of read performance to be able to write over 7 times faster!