An Xserve RAID can be split into multiple logical units, referred to as a LUN. Each side, or channel, of the RAID is, by default a single LUN. You can use the RAID Admin utility (located at /Applications/Server) to format each of these as multiple LUNs if you wish. When the LUNs are formatting (which generally takes 48 hours) you will start to see them in disk utility. Do not assign a file system to them yet if you are to use them with Xsan. Instead you will use the cvlabel command to label each of your LUNs, which marks them as able to be used by Xsan.