The SAN Era Takes Shape.The era of Storage Area Networks (SANs) has started to take shape. A SAN is a dedicated network that connects all the servers and clients to a shared pool of storage devices. The pool consists of servers, external storage devices, hubs and switches, along with network and storage management tools. The SAN concept is being fueled primarily by advances in Fibre Channel, but can be constructed from SCSI SCSI in full Small Computer System Interface Once common standard for connecting peripheral devices (disks, modems, printers, etc.) to small and medium-sized computers. SCSI has given way to faster standards, such as Firewire and USB. , SSA (Serial Storage Architecture) A fault tolerant peripheral interface from IBM that transfers data at 80 and 160 Mbytes/sec. SSA uses SCSI commands, allowing existing software to drive SSA peripherals, which are typically disk drives. , ESCON (Enterprise Systems CONnection) An IBM S/390 fiber-optic channel that transfers 17 Mbytes/sec over distances up to 60 km depending on connection type. ESCON allows peripheral devices to be located across large campuses and metropolitan areas. , and FICON (FIber CONnector) An IBM mainframe channel introduced with its G5 servers in 1998. Based on the Fibre Channel standard, it boosts the transfer rate of ESCON's half-duplex 17MB/sec to a full-duplex 100MB/sec. I/O interfaces. In a Fibre Channel SAN, a variety of servers connect to a variety of storage devices via the Fibre Channel fabric A Fibre Channel fabric (or Fibre Channel switched fabric, FC-SW) is a switched fabric of Fibre Channel devices enabled by a Fibre Channel switch. Fabrics are normally subdivided by Fibre Channel zoning. Each fabric has a name server and provides other services. . Fibre Channel Arbitrated Loop (FCAL) architecture allows for up to 126 devices per loop, but throughput drops as devices are added because each node represents a latency factor against total loop performance. The attached storage devices form a pool and are externalized from the individual servers, allowing a large-scale storage subsystem to be shared among multiple host servers. Through a SAN, large numbers of users can simultaneously access data stored on a network of storage devices. Obviously, data sharing capabilities will become fundamental to the future of the SAN and management middle-ware will be key to its overall success. This architecture eliminates the bandwidth load caused by data transfers between servers and storage systems using slower network interfaces from the LAN (Local Area Network) A communications network that serves users within a confined geographical area. The "clients" are the user's workstations typically running Windows, although Mac and Linux clients are also used. . The SAN storage devices can be disk arrays, tape devices and libraries, and tape or optical drives. In a SAN, the devices are not dedicated to any specific server enabling storage to be added as needed without disrupting server availability. The SAN architecture separates network traffic onto LANs and data traffic onto SANs. SANs have gained notable industry momentum and excitement. They hold expectations to evolve toward global storage management capabilities and are expected to combine with NAS (1) See network access server. (2) (Network Attached Storage) A specialized file server that connects to the network. A NAS device contains a slimmed-down operating system and a file system and processes only I/O requests by supporting the popular servers to become the ISAN--Intelligent Storage Area Network. We have just begun the SAN journey and many issues remain, including where the brains or management capability of the SAN, a SAN Operating System, will ultimately be located. The SAN model will lead the drive to fulfilling the long-awaited information utility promise. |
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