Storage Area Network(SAN)

Storage Area Network (SAN) attaches computer storage device such as disk array controllers and tape libraries to servers. The SAN network allows data transfers between computers and disks at the same high speeds as when they are directly attached. SAN consists of a communication infrastructure, which provides physical connection and a management layer, which organizes the connection, storage elements and computer systems.
Just as a LAN can be used to connect clients to servers, a SAN can be used to connect servers to storage, servers to each other and storage to storage. A SAN does not need to be a physically separate network; either it can be a dedicated sub network, carrying only the business-critical I/O traffic between servers and storage devices. In a SAN, a storage device is not the exclusive property of any one server rather the infrastructure of SAN works in a way that makes all storage devices available to all servers on a LAN or WAN. As more storage devices are added to a SAN, they too will be accessible from any server in the larger network.

How San Started

SAN evolved from the concept of taking storage devices and storage traffic off the LAN and creating a separate back-end network designed specifically for data. Traditionally, on client server systems, data was stored on devices either inside or directly attached to the server. Next came Network Attached Storage (NAS) which took the storage devices away from the server and connected them directly to the network. SAN take the principle one step further by allowing storage devices to exist on their own separate network and communicate directly with each other over very fast media. Basically there are three types of SAN at present Centralized SAN, distributed SAN, and IP SAN.
A centralized SAN connects multiple servers to a collection of disks where as a distributed SAN typically uses one or more Fiber Channel or SCSI switches to connect nodes within buildings or campuses. Another SAN option is IP storage, which enables data transfer via IP over fast Gigabyte Ethernet locally or via the Internet to anywhere in the world. Although there are wide variety of SAN available in the market but due to its complexity and high pricing it has not been widely used.

Whos is using it?
SAN is now being used in large scale, high performance enterprise storage operations. The IP SAN technology is expected to eventually produce cheap SAN, but it is unlikely that this technology will be used outside the enterprise data center environment. San is being popular in SOHO market which was largely occupied by NAS. As SAN is a complex technology it is wise to know the requirements and issues related to SAN design and implementation.

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