Storage area network (SAN) is a high-speed sub-network of shared storage devices. It contains nothing but disks for storing data. A SAN's architecture works in a way that makes all storage devices available to all servers on a LAN or WAN. It is an architecture to attach remote computer storage devices such as disk arrays, tape libraries, etc. to servers such that the devices appear as locally attached to the operating system. Because stored data does not reside directly on any of a network's servers, server power is utilized for business applications, and network capacity is released to the end user.
Devices on the SAN are normally connected together through a special kind of switch, called a Fiber Channel switch, which performs basically the same function as a switch on an Ethernet network, in that it acts as a connectivity point for the devices. Because Fiber channel is a switched technology, it is able to provide a dedicated path between the devices in the fabric so that they can utilize the entire bandwidth for the duration of the communication.
Sharing storage usually simplifies storage administration and adds flexibility since cables and storage devices do not have to be physically moved to move storage from one server to another. Other benefits include the ability to allow servers to boot from the SAN itself. This allows for a quick and easy replacement of faulty servers since the SAN can be reconfigured so that a replacement server can use the LUN of the faulty server.
SANs also tend to enable more effective disaster recovery processes. A SAN could span a distant location containing a secondary storage array. This enables storage replication either implemented by disk array controllers, by server software, or by specialized SAN devices.