sorry but there's quite a bit of out of date and basically incorrect information in the answers before. I've been working with sql server on storage area networks since SQL 2000 and I can say that unless you're very lucky the storage will not be set up correctly to give optimum results for SQL Server.

The type of SAN will also play a part in this as will the underlying configuration of the disks. The exact requirements for yourself will depend upon the application(s) which drive the databases(s) and the usage pattern. I currently support a system which has users in 80+ countries, this presents particular issues around maintenence windows ( there are none! ).

I'd say it was probably far easier to get a really bad setup on a SAN than on DAS.

You should talk to the storage provider and ask for any white papers they have on deploying databases on their storage. About the only general consideration I'd say was generic was to try to get a dedicated pool of disks for your SQL Server - if you physically share the spindles with other applications it's most likely you'll suffer contention.

here's some blog posts I did on storage testing - there's a few links to my website too on these. I also did some vendor specific testing with 3PAR so if you have their hardware I can provide some specific information.

http://sqlblogcasts.com/blogs/grumpyolddba/archive/2008/10/07/testing-times-1.aspx

http://sqlblogcasts.com/blogs/grumpyolddba/archive/2008/10/13/testing-times-2.aspx

http://sqlblogcasts.com/blogs/grumpyolddba/archive/2008/11/23/Testing-Times-3-_3B00_-Benchmarking-SQL-Server.aspx

http://sqlblogcasts.com/blogs/grumpyolddba/archive/2009/05/04/storage-the-final-frontier.aspx

http://sqlblogcasts.com/blogs/grumpyolddba/archive/2009/01/14/tracking-contention-on-the-san-testing-times.aspx

good luck!