I'm not going to go into too much depth here as I have written a couple of papers a while back on this subject. Instead I would encourage you to download these two papers, read them, and tell me what you think.

This first paper takes a quick look at Oracle's orion workload tool and how to use it. It is good intro material for anyone who has to architect storage for an Oracle database.
The Optimal Oracle Configuration: Using the Oracle Orion Workload Tool to Accurately Configure Storage

This second paper takes a look at how I did some ORION workload test on a very large SAN and the results. Over 100 hours of testing and well worth the read.
BOSS: Performance and Scalability of the 6998 Storage System