I have worked with medium to large databases in SQL Server and Oracle for some time and have seen just about any combination of disks you can imagine for them. When our financial system went from RAID 5 to RAID 10, the disk queues shank 40% and IO improved more than imaginable. We got to be heroes once the move was finished. At the time it was an IO intensive 50GB database with about 800 users.

Our POS system, which is Microsoft front to back, was crippled by an oversized RAID 5 array. We switched it to a RAID 10 array and did nothing else. The fix got reports from a 30 hour run to a six minute run. When we redistributed the files to improve the IOPS things got even better. Nothing changed but the disk configuration. The system works now like it should.

As hardware has gotten better the gap has narrowed some. The question you have to ask is, "How important is my data?" I want our people to get their data instantly every time. I don't want anyone to have to wait for information they need to make our organization work.