Hi We are running Exchange 2003 SP2 on a SAN and trying to figure out how big the LUN's should be. Couple of questions: i) Each SG has the full number of databases (i.e. 5), and we have the full number of SG's (i.e. 4). Is there an issue with placing all 20 stores on the same LUN, or would it be better to split them up...and, if so, why?ii) Our mailbox limit is 100MB per user. We have about 160 users per Store....is there any way to work out how big each database would actually get to as the maximum size? iii) Should transaction logs be placed on the same LUN or different? If so, why?

How many users? First Database Files and the Transaction logs should be on seperate Luns for Each database. This helps with performance, troubleshooting, recovery. See here: Best Practices for Configuring Exchange Back-End Storagehttp://technet.microsoft.com/en-us/library/bb124123(EXCHG.65).aspxGiven the number of databases/storage groups I would recommend mount points over drive letters. As for Question 2 you could leverage the Exchange Storage Calculator.SF - MCITP:EMA, MCTS