STORAGE AREA NETWORK

STORAGE AREA NETWORK (SAN):

SAN is an architecture to attach remote computer storage devices (such as disk arrays, tape libraries, and optical jukeboxes) to servers in such a way that the devices appear as locally attached to the operating system. Its a network whose primary purpose is the transfer of data between computer systems and storage elements. A san consists of a communication structure , which provides physical connections; and a manager layer, which organises the connections, storage elements , and computer systems so that the data transfer is secure.
A storage area network (SAN) is a high-speed special-purpose network (or subnetwork) that interconnects different kinds of data storage devices with associated data server on behalf of a larger network of users. Typically, a storage area network is part of the overall network of computing resources for an enterprise. A storage area network is usually clustered in close proximity to other computing resources such as IBM z990 mainframe but may also extend to remote locations for backup and archival storage, using wide area network carrier technologies such as ATM or SONET.

A san can also be a storage system consists of storage elements, storage devices, computer systems, or appliances, plus all controll softwares, communicating over a network.
A san is a high speed network attaching high speed servers and storage devices. A san always any-to-any connections across the network, using interconnected elements such as routers, gateways, hubs, switches, and directors. a san can be shared between servers or dedicated to one server. It can be local or can be extended over a geographical distances.
San create new methods of data storage to the servers(both in availability and performance).
San facillitates direct, high –speed data transfers between servers and storsge devices in three ways-

1.Server to storage – this is the model of interaction with the storage devices.
2.server to server- used for high volume communication between seervers.
3.storage to storage-this movement capability enables data to be moved without server intervention.



Historically, data centers first created "islands" of SCSI DISK ARRAYS as Direct Attached Servers (DAS), each dedicated to an application, and visible as a number of "virtual hard drives" (i.e. LUNs). Essentially, a SAN consolidates such storage islands together using a high-speed network.
Operating systems maintain their own file systems on them on dedicated, non-shared LUNS, as though they were local to themselves. If multiple systems were simply to attempt to share a LUN, these would interfere with each other and quickly corrupt the data. Any planned sharing of data on between computers within a LUN requires advanced solutions.
Despite such issues, SANs help to increase storage capacity utilization, since multiple servers consolidate their private storage space onto the disk arrays



Sharing storage usually simplifies storage administration and adds flexibility since cables and storage devices do not have to be physically moved to shift storage from one server to another.
Other benefits include the ability to allow servers to boot from the SAN itself. This allows for a quick and easy replacement of faulty servers since the SAN can be reconfigured so that a replacement server can use the lun of the faulty server. This process can take as little as half an hour and is a relatively new idea being pioneered in newer data centres.


SAN infrastructure



SAN-switch with optical fibre channel connectors installed.


SANs often utilize a Fibre Channel fabric topology - an infrastructure specially designed to handle storage communications. It provides faster and more reliable access. A fabric is similar in concept to a network segment in a local area network. A typical Fibre Channel SAN fabric is made up of a number of Fibre Channel switches.
Today, all major SAN equipment vendors also offer some form of Fibre routing solution, and these bring substantial scalability benefits to the SAN architecture by allowing data to cross between different fabrics without merging the data.


Compatibility

One of the early problems with Fibre Channel SANs was that the switches and other hardware from different manufacturers were not entirely compatible. Although the basic storage protocols FCP were always quite standard, some of the higher-level functions did not interoperate well. Similarly, many host operating systems would react badly to other operating systems sharing the same fabric. Many solutions were pushed to the market before standards were finalized and vendors have since innovated around the standard.


SANs at home

A SAN, being a network of large disk arrays, is primarily used in large scale, high performance enterprise storage operations. SAN equipment is relatively expensive and so fibre channel host bus adapters are rare in desktop computers. The iSCSI SAN technology is expected to eventually produce cheap SANs, but it is unlikely that this technology will be used outside the enterprise data center environment.

SANs in media and entertainment

Video editing workgroups require very high data transfer rates. Outside of the enterprise market, this is one area that greatly benefits from SANs.
Per-node bandwidth usage control, sometimes referred to as Quality of Service (QoS), is especially important in video workgroups as it ensures fair and prioritized bandwidth usage across the network if there is insufficient open bandwidth available. Avid Unity, Apple's Xsan and Tiger Technology MetaSAN are specifically designed for video networks and offer this functionality.








References
"TechEncyclopedia:IPStorage". http://www.techweb.com/encyclopedia/defineterm.jhtml?term=IPstorage.

Retrieved 2007-12-09.
"TechEncyclopedia:SANoIP". http://www.techweb.com/encyclopedia/defineterm.jhtml?term=SANoIP. Retrieved 2007-12-09.
Wikepedia.
IBM storage area network article.