Definition

A storage area network (SAN) is defined as a set of interconnected devices (for example, disks and tapes) and servers that are connected to a common communication and data transfer infrastructure such as Fibre Channel. The common communication and data transfer mechanism for a given deployment is commonly known as the storage fabric. The purpose of the SAN is to allow multiple servers access to a pool of storage in which any server can potentially access any storage unit. Clearly in this environment, management plays a large role in providing security guarantees (who is authorized to access which devices) and sequencing or serialization guarantees (who can access which devices at what point in time).

SANs evolved to address the increasingly difficult job of managing storage at a time when the storage usage is growing explosively. With devices locally attached to a given server or in the server enclosure itself, performing day-to-day management tasks becomes extremely complex; backing up the data in the datacenter requires complex procedures as the data is distributed amongst the nodes and is accessible only through the server it is attached to. As a given server outgrows its current storage pool, storage specific to that server has to be acquired and attached, even if there are other servers with plenty of storage space available. Other benefits can be gained such as multiple servers can share data (sequentially or in some cases in parallel), backing up devices can be done by transferring data directly from device to device without first transferring it to a backup server.

So why use yet another set of interconnect technologies? A storage area network is a network like any other (for example a LAN infrastructure). A SAN is used to connect many different devices and hosts to provide access to any device from anywhere. Existing storage technologies such as SCSI are tuned to the specific requirements of connecting mass storage devices to host computers. In particular, they are low latency, high bandwidth connections with extremely high data integrity semantics. Network technology, on the other hand, is tuned more to providing application-to-application connectivity in increasingly complex and large-scale environments. Typical network infrastructures have high connectivity, can route data across many independent network segments, potentially over very large distances (consider the internet), and have many network management and troubleshooting tools.

A storage area network (SAN) is a 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. Although the cost and complexity of SANs are dropping, they are uncommon outside larger enterprises
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 centers. There are a number of emerging products designed to facilitate and speed this up still further. Brocade, for example, offers an Application Resource Manager product which automatically provisions servers to boot off a SAN, with typical-case load times measured in minutes. While this area of technology is still new many view it as being the future of the enterprise data center