My guess is that the SQL service is starting before the disks are available. If you check the error log, you'll probably find a lot of errors relating to SQL unable to find/access the data files.
Check the error logs, see if that is the case.
What IO subsystem are you running on?
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability