| Are you sure you're talking about SAN fabrics? The vendors are pretty far from proprietary in implementation into a cluster. It's either ISCSI or FC for the most part, every OS has initiators for both, and the filesystem used is nearly always completely abstract to the SAN device itself. That being said, many of the currently available cluster filesystems leave a lot to be desired. GFS/GFS2 for example, which is the prevailing/recommended solution for Linux, has a tiresome locking/fencing layer to it. Not only is it sort of a pita to set up and to add/remove cluster members, but to achieve the performance that most SAN devices can deliver in a task that can saturate the systems involved, many people need to set up an infiniband network JUST for the lock manager or that becomes the bottleneck.
Note that a basic difference between a SAN and a NAS is that a SAN is intended for use by many systems all accessing(and modifying) the same data. | 