A storage area network (SAN) is a dedicated high-speed network (or subnetwork) that interconnects  and presents shared pools of storage devices to multiple servers.

A SAN moves storage resources off the common user network and reorganizes them into an independent, high-performance network. This allows each server to access shared storage as if it were a drive directly attached to the server. When a host wants to access a storage device on the SAN, it sends out a block-based access request for the storage device.

A storage area network is typically assembled using three principle components: cabling, host bus adapters (HBAs) and switches. Each switch and storage system on the SAN must be interconnected and the physical interconnections must support bandwidth levels that can adequately handle peak data activities.

Storage area networks are managed centrally and Fibre Channel SANs have the reputation of being expensive, complex and difficult to manage.  The emergence of iSCSI has reduced these challenges by encapsulating SCSI commands into IP packets for transmission over an Ethernet connection, rather than a Fibre Channel connection. Instead of learning, building and managing two networks -- an Ethernet local area network (LAN) for user communication and a Fibre Channel SAN for storage -- an organization can now use its existing knowledge and infrastructure for both LANs and SANs.

SAN Implementation;
To set up a simple SAN, you need only three major components: a SAN switch, a storage device and a server. You'll also require cables to connect the various elements together and SAN management software. In most real-world settings, a SAN will include many different switches, storage devices and servers, and it will likely also include routers, bridges and gateways to extend the SAN over large areas and to connect to other parts of the data center network. The SAN's topology will depend on its size and the needs of the organization.

The process of deploying a SAN requires several steps. First, you need to design your SAN, taking into account your current needs and future scalability requirements. Second, you'll need to select a vendor or vendors to provide the hardware and software you'll need, as well as any related services. Next, you'll install the necessary hardware and then install and configure the software for managing your SAN. Deploying a SAN is a complicated process that often requires specialized knowledge and a great deal of planning, particularly if your SAN is very large.