there is a big difference between NAS and SAN. the main idea of SAN is to take the storage-traffic away from the ethernet (!). you create an own network with high performance for that stuff, only for that stuff. the SAN also use switches, but they are special SAN-switches like McData of Brocade (supported is FC-AL and FC-fabric):
http://www.sun.com/storage/san/infra...brocade/24000/
there could be an storage-box like perderabo said: EMC/SHARK/HDS
http://www.sun.com/storage/highend/9980/index.xml
that type of box creates LUNs which can be accessed threw more than one host, splitted in zones and groups addressed by mulipathing ways to the devices. there could be an centralised tape libery:
http://www.sun.com/storage/tape/l6000/index.xml
the main feature is that you can act with these devices like they are directly attached like a SCSI-box. you are also talking to these by the SCSI-protocol applied to the FC-protocol. SAN supports heterogeneous hosts on one device. they don't use IP-addresses they use WWN-addr for identification.
you should take some minutes and google for it.... i think its the way to the future...
gP