There's a new whitepaper on TechNet that I've just come across (even though it was published 6 months ago!) called Predeployment I/O Best Practices. It's really good - discussing the following:

• Guidelines for determining I/O capacity
• Disk configuration best practices and common pitfalls
• Using SQLIO to determine capacity and interpreting its results
• Using System Monitor to monitor an IO subsystem

You can read it here and I've added a link to our whitepapers page.

While I'm on the subject of I/O, Bob Dorr (A Senior Escalation Engineer in PSS) published a blog post last year that debunks a couple of urban legends around SQL Server's IO, specifically:

• The myth that SQL Server used one thread per data file
• The myth that a disk queue length greater than 2 indicates an I/O bottleneck

Check out his blog post and the subsequent discussion here.