Storage Area Networks (SAN)

SANs firstly originated to overcome the problems with Network Attached Storage (NAS) devices, which like ordinary servers are difficult to manage and expand the capacity on. NAS devices also add to the traffic on the network and suffer from the delays introduced by the operating systems, network stacks.
A SAN is made up of a number of fabric switches connected in a network. The
most common form of SAN uses the fibre channel protocol (with Fibre Channel switches). Alternatively ISCSI could be used with IP switches. Connected to the SAN will be one or more disk array controllers and one or more servers. The SAN allows the storage space on the hard disks in the Disk array controllers to be shared amongst the servers.
A SAN gives the ability to take all the disk drives off all mainframes and servers, then concentrate the drives in a single location, and allow all the servers to read and write to any combination of the drives simultaneously. As its name implies, a SAN is its own network, based on fiber channel technology.

Fibre channel technology is capable of very high bandwidths, matching the ability of high-performance disk drives to transfer data at their highest sustained rates. But unlike computer buses and SCSI chains, fiber channel can be extended to very large campuses. A SAN based on 9mm fiber optics can extend to a 10km diameter.

Every server that is part of the SAN normally has a fiber channel interface to connect inward to the SAN and a local network interface to connect outward to a conventional local area network (LAN). The SAN switches are capable of connecting every server to every storage device on the SAN, at fiber channel speeds. Above all, a SAN offers very high data transfer rates from disk to server and directly from disk to disk. SANs transfer data at 100MBps. The current speed of 100MBps is comparable to the speed of a gigabit Ethernet but has the immense advantage(compared to a LAN) that every server has intimate access to every storage device.