A SAN is a high-speed network connecting servers and storage devices, and dedicated exclusively to the transfer of data between them. It is thus sometimes referred to as "the network behind the servers". A SAN eliminates the traditional concept of individual servers "owning" and managing finite volumes of locally attached storage, introducing instead the flexibility of networking to enable one or more servers to share a common storage facility consisting of one or more storage devices, some or all of which may be located remotely from the servers that use it.

A SAN consists of a physical communication infrastructure (cabling, routers, hubs, switches, gateways, etc) and a management layer which organises the connections, servers and storage devices so that data transfer is secure and robust. The two most common types of SAN are the Fibre Channel SAN which uses Fibre Channel networking and the iSCSI SAN which uses TCP/IP networking. A third SAN technology is ATA over Ethernet (AOE), which runs directly over Ethernet without using an intermediate protocol such as TCP/IP. The term SAN is typically associated with making block I/O services available on a network, rather than the file access services typically provided by NAS devices.

A SAN bypasses traditional network bottlenecks by enabling direct, high-speed, "any-to-any" data transfers between servers and storage devices in three ways:

• Server to storage: the traditional model of server/storage interaction, the advantage being that a single storage device may now be accessed concurrently by multiple servers.
• Server to server: high-speed, high-volume communications between servers.
• Storage to storage: movement of data from one storage device to another without server intervention, thereby freeing up server processor cycles. For example, a disk device can back itself up to a tape device, or mirror itself to another remote device, across the SAN without server intervention.