Storage Area Networks (SAN)

Storage Area Networks (SAN)

A storage area network is a high-speed special-purpose network or subnetwork that interconnects different kinds of data storage devices like Fabric Switches, RAIDs, Tape Libraries, Host servers, Host Bus Adapters. Typically, a storage area network is part of the overall network of computing resources for an enterprise.

A storage area network can use existing communication technology such as IBM's optical fiber ESCON or it may use the newer Fibre Channel technology. Some SAN system integrators liken it to the common storage bus (flow of data) in a personal computer that is shared by different kinds of storage devices such as a hard disk or a CD-ROM player.

SANs (storage area networks) support disk mirroring, backup and restore, archival and retrieval of archived data, data migration from one storage device to another, and the sharing of data among different servers in a network. SANs can incorporate subnetworks with NAS (network attached storage) systems.

A Storage Area Network can also be a storage system consisting of storage elements, storage devices, computer systems, and/or appliances, plus all control software, communicating over a network.

Fabric Switch

Fibre Channel is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committe of the InterNational Committee for Information Technology Standards an American National Standards Institute (ANSI)–accredited standards committee. It started for use primarily in the supercomputer field, but has become the standard connection type for storage area networks (SAN) in enterprise storage. Despite common connotations of its name, Fibre Channel signaling can run on both twisted pair, copper wire and fiber-optic cables.

Fibre Channel Protocol (FCP) is the interface protocol of SCSI on the Fibre Channel.

RAID

RAID stands for "redundant array of independent disks" (originally "redundant array of inexpensive disks"). It refers to technology that coordinates multiple disks to behave as a single unit. Most RAID implementations accomplish this through a technique called striping. A stripe is a disk segment varying in size from one sector (usually 512 bytes) up to several megabytes. The stripes of the independent disks are re-ordered to distribute disk usage across all of them.

Tape Library

A Tape Library (sometimes called a tape silo or tape jukebox) is a storage device which contains one or more tape drives, a number of slots to hold tape cartridges, a barcode reader to identify tape cartridges and an automated method / robot for loading tapes.

These devices can store immense amounts of data, currently ranging from 20 terabytes up to several petabytes of data or about ten thousand times the capacity of a typical hard drive and well in excess of capacities achievable with

For large data-storage, they are a highly cost-effective solution at least 60% less than most hard drives, and they also add the value of providing systematic access to very large quantities of data. The tradeoff for their larger capacity is their slower access time, which usually involves mechanical manipulation of tapes. Access to data in a library takes from several seconds to several minutes.

Because of their slow random access and huge capacity, tape libraries are primarily used as the final stage of data archiving. A typical application would be a large organization saving extensive transaction record histories for legal or auditing purposes. Once the tape library is full, old dat is progressively overwritten by new data.

Smaller tape libraries with only one drive and robot are known as autoloaders.

Host Servers

Host servers attached to the storage area networks are categorised as san attached hosts and these include host servers from vendors like Windows, HP-UX, IBM-AIX, Linux and Unix.

Host Bus Adapters (HBA)

A host controller, host adapter, or host bus adapter (HBA) connects a host system (the computer) to other network and storage devices. The terms are primarily used to refer to devices for connecting Fibre Channel, SATA, and SCSI devices, but devices for connecting to ESCON Ethernet and other systems may also be called host adapters. Recently, the advent of iSCSI has brought about Ethernet HBAs, some including TCP Offload Engines, Firewire and USB also use host controllers.

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