What is SAN?
The proper definition of Storage Area Network (SAN) is a dedicated high-speed network that allows fast, reliable access among servers and external or independent storage resources. Specifically, it interconnects different kinds of data storage devices with associated data servers on behalf of a larger network of users and allows these storage devices to be shared among multiple hosts without affecting system performance.
The most important component is that these storage devices are interfaced to the network through components like switches that provide dynamic any-server to any-storage solutions. Storage Area Network actually makes a paradigm shift from the conventional methods of network storage where all the subsystems, software and hardware related to storage are moved off the server and take the form of a separate sub-network within organizations network structure. This network can use existing communication technology such as IBM's optical fiber ESCON or it may use the newer Fibre Channel technology.
SNIA definition of SAN
According to Storage Networking Industry Association (SNIA), the primary purpose of Storage Area Network is the transfer of data between computer systems and storage elements and among storage elements. A Storage Area Network consists of a communication infrastructure, which provides physical connections, and a management layer, which organizes the connections, storage elements, and computer systems so that the data transfer is secure and robust.
A storage system consists of storage elements, storage devices, computer systems, plus applications and all control software, communicating over a network. Nevertheless, the SNIA definition specifically does not recognize the term SAN with Fibre Channel technology. When the term SAN is used in correlation with Fibre Channel technology, it is preferable to use term "Fibre Channel SAN".