the "original" SAN network uses switches that use a dedicated SAN protocol like Fiber-Channel,
this is not compatible with ethernet packets, so these types of switches are not interchangeable.
later there became iSCSI, iSCSI over ethernet, fiber channel over ethernet and other protocols that are compatible with "normal" LAN-switches.
this has the advantage that you do not need to install two physical separate networks.
you can use the same hardware devices for both LAN and SAN,
you can even us the same switch for both while separating data using different VLANs.
