Bob Dorr strongly recommended to use 64KB cluster size regardless whether your underlying disks are on SAN or direct attached because though your block size is 64KB at the OS level and when that I/O request gets to SAN , it depends on how the SAN treats there block size. Differs with every SAN, for ex the minimum block request size for IBM SAN is 1GB. More details can be found here https://blogs.msdn.microsoft.com/psssql/2010/03/24/how-it-works-bob-dorrs-sql-server-io-presentation/ [/url].