One other thing is to check how the data is striped to the SAN. With a SAN, the drives can have a particular stripe size and the OS on the server can write to those drives with another stripe size. One site of our company ended up with 100% fragmentation across all drives...definately a slow-down.

Since there are differing opinions on how to stripe the drives, you will need to make your own educated guess. Microsoft recommends 64k stripe size for running SQL Server. Other companies' software running on top of SQL Server suggest different sizes.

We have found that 64k works for us. Even though SQL writes in 8k blocks.

Michelle