Frank, > You definitely DO NOT want to do RAID 5 on a database server. That > is probably the worst setup you could have, I've seen it have lower > performance than just a single hard disk. I've seen that on RAID0 and RAID10 as well. This is more about the quality and modernity of the RAID controller than anything else at this point, although there are some theoretical advantages of RAID10 from a random seek standpoint even if the adapter CPU is infinitely fast at checksumming. We're using RAID5 in practice for OLAP / Data Warehousing systems very successfully using the newest RAID cards from 3Ware (9550SX). Note that host-based SCSI raid cards from LSI, Adaptec, Intel, Dell, HP and others have proven to have worse performance than a single disk drive in many cases, whether for RAID0 or RAID5. In most circumstances I've seen, people don't even notice until they write a message to a mailing list about "my query runs slowly on xxx dbms". In many cases, after they run a simple sequential transfer rate test using dd, they see that their RAID controller is the culprit. Recently, I helped a company named DeepData to improve their dbms performance, which was a combination of moving them to software RAID50 on Linux and getting them onto Bizgres. The disk subsystem sped up on the same hardware (minus the HW RAID card) by over a factor of 10. The downside is that SW RAID is a pain in the neck for management - you have to shut down the Linux host when a disk fails to replace it. - Luke
