My Summary: A NAS is just a filestore. It is just like a shared external hard drive. It is accessed as a shared drive and accessed like \\NAS-Server\folder1.
A SAN is also like that, but is accessed as a disk, and computers (servers) connecting to the SAN are allocated certain amounts of storage. They deal with the SAN as they would with a disk, in blocks. That allocation can change, so the storage is in a sense, virtualized. Computers have storage, and by expanding the SAN, you can allocate more space however you wish, to the computers accessing the SAN. So how do you access the SAN? iSCSI is one way - it just means using existing ethernet to access the SAN. It is lower performance and lower cost than alternate means. Fibre Channel is currently faster at around 4 GB/s. Duration : 0:8:26