(Storage Area Network) A network of storage disks. In large enterprises, a SAN connects multiple servers to a centralized pool of disk storage. Compared to managing hundreds of servers, each with their own disks, SANs improve system administration. By treating all the company's storage as a single resource, disk maintenance and routine backups are easier to schedule and control. In some SANs, the disks themselves can copy data to other disks for backup without any processing overhead at the host computers.
The SAN network allows data transfers between computers and disks at the same high peripheral channel speeds as when they are directly attached. Fibre Channel is a driving force with SANs and is typically used to encapsulate SCSI commands. SSA and ESCON channels are also supported.
Centralized or Distributed
A centralized SAN connects multiple servers to a collection of disks, whereas a distributed SAN typically uses one or more Fibre Channel or SCSI switches to connect nodes within buildings or campuses. For long distances, SAN traffic is transferred over ATM, SONET or dark fiber. To guarantee complete recovery in a disaster, dual, redundant SANs are deployed, one a mirror of the other and each in separate locations.
Another SAN option is IP storage, which enables data transfer via IP over fast Gigabit Ethernet locally or via the Internet to anywhere in the world (see IP storage). See LAN free backup.
Channel Attached Vs. Network Attached
A related storage device is the network attached storage (NAS) system, which is a file server that attaches to the LAN like any other client or server in the network. Rather than containing a full-blown operating system, the NAS uses a slim microkernel specialized for handling only file reads and writes (CIFS/SMB, NFS, NCP). However, the NAS is subject to the variable behavior and overhead of a network that may contain thousands of users. See block level.
SAN by EMC , HP ,IBM etc