A pet hate of mine is when people refer to a Storage Device, such as a Fibre Attached NetApp Filer, as a SAN. It is not a SAN but a storage device that connects to a SAN. I often hear people say “Oh, you have bought a new SAN” when actually you have bought an additional Storage Device to connect to your existing SAN.
If you think about a network, or a LAN (Local Area Network), you have Servers connected to the LAN providing services to clients also connected to the LAN as depicted in the following diagram.
Similarly a storage device connects to a SAN (Storage Area Network) to provide services to other devices such as storage for servers, as depicted in the following diagram
More often than not there will be two SANs for redundancy, in a Fibre Channel setup these are commonly referred to as SAN fabrics. The following diagram illustrates this.
So in a Storage Area Network (SAN) environment you Storage Devices are like the Servers on your LAN and the Servers connected to your SAN are like the clients in your LAN environment. The LAN and the SAN are combined with the Servers being the common element, i.e. the Servers are connected to the front end LAN providing services to the clients but are also connected to the backend SAN using services from the Storage Devices as depicted in the following diagram.