Exchange SAN allocation size

Sean has been configuring his SAN for his Exchange 2003 implementation and wondered about our disk allocation unit sizes.  His SAN vandor insisited that he had to use 64k which puzzled me a little so I did some research.   From the Optimising storage for Exchange document, 4k is the recommended unit size.  it sounds like his disk is a bit hungry, so Sean needs to do some performance analysis on the disk subsystem.  That’s probably why he’s been recommended to use 64k.  He may also need to plan how many disks are used per server and test the perormance of the SAN using Jetstress from here