We determined that we needed an external disk system that would present a "volume" to the modular server, not just a hardware connection. This means we will need different hardware (more expensive) than what we have now.
see the Tested Hardware and Operating System list for the list of peripherals that can be attached to the external SAS port
Also see instructions on connecting a VTrak, for example - http://www.intel.com/support/motherboards/server/sb/CS-029660.htm
We got a VTrak system, works great!