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Fibre Channel

At one time, some engineers regarded Fibre Channel as the successor to the SCSI Parallel Interface for high-performance disk drives. Although it has been used successfully in many drive products, it has yet to earn the following of the other interfaces. The steady advance in the speeds of other interfaces has severely eroded its edge in performance. Both AT Attachment and the latest versions of parallel SCSI outrace Fibre Channel's 100MBps capabilities. Among personal computers, it remains a viable, but not popular, interface.

The current implementation of Fibre Channel used for mass storage systems is actually a specialized derivative subset of the technology called Fibre Channel Arbitrated Loop (FC-AL). Although even this slice of the standard allows a variety of cabling options, including twinaxial, coaxial, and optical connections, its chief use in mass storage currently is as a backplane interface. That is, FC-AL drives link directly to printed circuit boards in their computer hosts without any cabling between.

At that level, you don't have to understand FC-AL to use it. If you are physically capable of putting a drive in a bay, you've mastered all you need to know. In modern computers, the drives and interface are self-configuring and should require no intellectual intervention on your part.

Development of FC-AL began in 1992 with the creation of the Fibre Channel Systems Initiative, a group of three leading workstation manufacturers (Hewlett-Packard, IBM, and Sun Microsystems) with the specific goal of overcoming the inherent problems with the SCSI Parallel Interface.

As with all modern serial systems, Fibre Channel is packet based. The same circuit and protocol that carry the data also handle all control information. Commands to retrieve a particular block from a disk drive, for example, are carried through the system as data in the form of standard SCSI-3 commands. The drive collects the packets sent for it, interprets them, and carries out the commands. It sends data back, when requested to, in the same data packet form.

Although with hard disk drives you'll probably only have to deal with the backplane connector, the Fibre Channel Arbitrated Loop specifications allow for a great variety of wiring systems. All FC-AL systems take the form of a loop, even the backplane connection. Each device in the loop has separate input and output connections. The output of one device connects to the next device in the loop, until the last device, which connects back to the first and completes the loop. Disconnecting a device from the loop may interrupt communications. Consequently, systems such as drive arrays that permit hot-swapping of devices have built-in port bypass circuits that route the loop signaling around the removed device.

The principal body governing the promotion and development of Fibre Channel standards is the Fibre Channel Association. You can get in-depth information about Fibre Channel, products using it, and meeting schedules, from the association at the following address:

Fibre Channel Association

12407 MoPac Expressway North 100-357

P.O. Box 9700

Austin, TX 78766-9700

Phone: 800-272-4618 or 512-328-8422

Fax: 512-328-8423

E-mail: fca@fibrechannel.com

The Fibre Channel Loop Community, a working group that's part of the association, is focused on the FC-AL standard. The address of the Fibre Channel Loop Community is as follows:

Fibre Channel Loop Community

P.O. Box 2161

Saratoga, CA 95070

Phone: 408-867-6630

Web site: www.symbios.com/fclc/fclcmain.htm

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