If you are running Xsan 1.3 on Mac OS X 10.4.5, Disk Utility will display Xsan volumes as unknown GPT partitions and will let you edit them.
Warning: Despite the fact that Disk Utility will allow it, you must not use Disk Utility to edit these volumes in Mac OS X 10.4.5, because doing so may cause data loss.
To avoid this risk, update your Xsan clients to Mac OS X 10.4.6 or later.
Using Disk Utility in Mac OS X 10.4.6 and later to edit Xsan volumes will not put data at risk, but in general you should use Xsan tools instead. Use Xsan Admin to label Xsan volumes, cvfsck to repair Xsan volumes, and Raid Admin to rebuild arrays.