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Storage Area Network

SANs are normally built on an infrastructure specially designed to
handle storage communications.
 Storage Area Network (SAN) is a high-speed subnetwork of shared storage
devices with associated data servers. Network is designed to attach storage
devices such as disk array controllers and tape libraries to multiple servers,
multiple paths are used to connect servers and storage systems
In a storage network, a server issues a request for specific blocks, or data
segments, from specific disk drives. This method is known as block storage.
The device acts in a similar fashion to an internal drive, accessing the specified
block, and sending the response across the network.
SAN's architecture works in a way that makes all storage devices available to 
required servers on a LAN or WAN. 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.
Basic Architecture of SAN is depicted below
Below is the layout of Enterprise Class HP SAN EVA
                                                          image copyright : hp
Main Components of a SAN
Drive Enclosure         --1
SAN Switches            --2
Controler Enclosure   --3
Controller Enclosure : A  pair of two interconnected controller modules that
control the physical disk array
Controllers : A hardware device with its own firmware that connects to the
Physical Drives and makes them available to host servers, also called as
 array controllers