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A storage area network (SAN) is a network of disk arrays, tape libraries or optical jukeboxes connected by network switches. The disks are attached to servers in such a way that the disks appear locally attached. The disk arrays can be housed in a remote data center, completely separate from the servers to which they are attached.
The storage component of a storage area network can be comprised of disk arrays, tape libraries or optical jukeboxes. Disk arrays are storage devices that contain multiple hard disks connected to a central controller. Tape libraries are devices that contain one or more tape drives and multiple tape cartridges. The tapes are loaded into the tape drives via a robot. Optical jukeboxes are similar to tape libraries but, instead of using tape drives and tape cartridges, they utilize optical drives and optical discs.
Most storage area networks are connected by fiber channel switches utilize the Fiber Channel Protocol to transport Small Computer System Interface (SCSI) commands over the network. The switches are connected using either twisted pair copper wire or fiber-optic cables. This type of cabling must be installed separately from the normal network infrastructure.
Storage area networks can also be connected through an Internet Protocol-based (IP-based) based technology called Internet Small Computer System Interface (iSCSI). An iSCSI solution can connect storage devices over a Local Area Network (LAN), a Wide Area Network (WAN) or over the Internet. Unlike fibere channel networks, the iSCSI networks do not require any special cabling. Instead, they use the existing network infrastructure.
A storage area network has its own file system. This file system allows the files on the SAN to be accessed by multiple servers using different operating systems. The file system is programmed in a way that minimizes the file storage and retrieval time. It also streamlines the management of the network and allows the network components to be scaled independently.
The use of a storage area network simplifies the administration of the storage devices. Multiple servers can access a single SAN. These servers can be set up to boot directly from the the SAN, which allows servers to be switched quickly. Cables and storage devices do not have to be moved in order to switch from one server to another.
Storage area networks are designed for disaster recovery. The network can span multiple remote locations. SANs also have built in data replication. This data replication keeps the SAN available even when a disk or a complete disk array fails.