In computing, a storage area network (SAN) is a network designed to attach computer storage devices such as disk array controllers and tape libraries to servers. As of 2006, SANs are most commonly found in enterprise storage.
A SAN allows a machine to connect to remote targets such as disks and tape drives on a network for block level I/O. From the point of view of the class drivers and application software, the devices appear as locally attached devices.
There are two variations of SANs:
1. A network whose primary purpose is the transfer of data between computer systems and storage elements. A SAN consists of a communication infrastructure, which provides physical connections, and a management layer, which organizes the connections, storage elements, and computer systems so that data transfer is secure and robust. The term SAN is usually (but not necessarily) identified with block I/O services rather than file access services.
2. A storage system consisting of storage elements, storage devices, computer systems, and/or appliances, plus all control software, communicating over a network.
For the rest of the Wikipedia entry on the above term, go here.
This Video from Google Video shows Adrian Bridgett giving a short talk on Storage Area Networks (SANs) This talk requires some knowledge of ethernet networking.