Hello...
in your case i would consider creating many luns especially for exchange server and the DB server (sql server?)
exchange server will have 3 luns on for OS one for DB and one for logs. i dont know for the specific storage if there are best practices to create the luns. beware lun misaligment cause it will cost you in performace and follow the best practices for exchange server and db especially when you create the partitions (not from disk mamagement) create them through disk part with create partition primary align=x (when x is the value of the starting partition offset)
consider also that 1 big raid whith many disks has more spindles so more performance.
there are many many scenarios you can follow to achieve max perf and reliability.