Fibre Channel Speeds Up

Making its move onto the data superhighway, the Fibre Channel promises to break the speed limit for serial data transmission

John Bryan

There's a new fast lane under construction on the data superhighway. Fibre Channel, a technology developed under the guidance and impetus of the ANSI X3T11 Fibre Channel committee and companies like Hewlett-Packard, IBM, and Sun Microsystems, promises high-speed serial data transmission over significant distances.

Microprocessors like the Pentium, PowerPC, and other RISC chips can deliver hundreds of MIPS to the desktop. However, their component subsystems cannot deliver data to these CPUs at anything close to processor capacity. Also, applications demand ever more resources. The result is an I/O bottleneck.

Although you may not find it in any c omputer design textbook, ``Amdahl's Law'' says that 1 Mbps of I/O capability is required for every MIPS of processor performance. Today's network technologies top out at about 100 Mbps, an order of magnitude slower than the fastest microprocessors.

Channel Speed vs. Network Flexibility

Two basic methods--channels and networks--are used for interprocessor communication. A channel is a direct point-to-point or switched communications link, predominantly hardware-based and designed for high speed. But a network is a heterogeneous collection of interconnected access points with a software structure that enables communication. The network approach allows many different types of data transfer, but the software overhead takes its toll in performance. Fibre Channel combines aspects of both types.

The ANSI group set ambitious goals for this new standard, including speeds of 133 to 1062 Mbps on a single fiber (either optical or metal cable), simultaneous bidirectional communication, support for distanc es of up to 10 km, small connectors made with off-the-shelf components, a variety of price/performance levels, and more. Perhaps most important was the decision to support several industry standard transport protocols, such as SCSI, IPI (Intelligent Peripheral Interface), HIPPI (High Performance Parallel Interface), and the IP portion of TCP/IP.

Fibre Channel Structure and Terminology

The Fibre Channel standard is defined in five separate layers, from the physical media (FC-0) to the highest-level protocol interfaces (FC-4). (See the text box ``Fibre Channel's Five-Layered Structure.'') A Fibre Channel installation has at least one link between two nodes (i.e., cable endpoints). Data flows between hardware entities called N_ports. Each node must have at least one N_port and generally has two, one inbound and one outbound; either may serve as originator, responder, or both. In addition, an N_port contains a Link_Control_Facility, a sort of firmware traffic cop that handles logical and physical contro l of the link.

Fibre Channel is a hardware-intensive, switched technology, with each port uniquely addressed by an N_port Identifier. Everything between the ports on the Fibre Channel is called the fabric--in most cases, a switch or series of switches provide the interconnects. Ports on the fabric are called F_ports. Hardware triggers in the frame header route control information--commands and responses--to control buffers, while sending data directly to memory allocated by the requesting task.

The Products

While few consumer products are yet available, many have been announced; chip- and component-level products are shipping. Cypress Semiconductor, Western Digital, AT&T, NCR, Vitesse Semiconductor, Triquint, AMCC, and Raytheon are all making chip sets for OEMs to use in Fibre Channel-based switches, interface cards, or disk products.

Dan Brown, vice president of the I/O Products Group at Western Digital, says the company will have a PCI (Peripheral Component Interconnect) host bus-ada pter card for Fibre Channel sampling in the fourth quarter.

Cypress--which also makes FPGAs (field programmable gate arrays), SRAM (static RAM), PROMs, and other logic devices--makes chip sets that support either copper or optical Fibre Channel communications (the specifications on the logic side of the wire are the same). Ed Grivna, principal engineer of Cypress's DataCom Division, explains what these logic components do: ``The biggest function of these parts are phase-lock loops, which are required on both the transmit and receive sides. On each Fibre Channel circuit, there is both a slow parallel side and a fast serial side. The parallel side talks to the device, while the serial side delivers [data] to the Fibre Channel. As data traffic passes through in either direction, phase-lock loops are used to synchronize the operations.''

Cypress, NCR, Raytheon, and Triquint currently make components that run at 266 Mbps only. Vitesse manufactures a 1-Gbps-only product. AMCC is the only vendor whose chip sets are compatible with all speed standards, but it cannot switch speeds dynamically; you must select one setting. All vendors of logic devices will be producing alternative rate chips in a year or so.

At the subsystem level, the first products are just beginning to hit the market. Early Fibre Channel market entries focus on I/O rather than on communications technologies, primarily because improving system I/O offers the greatest immediate benefits. The first products to debut are fast disk array subsystems, but LAN-type products will not be far behind. IBM and HP showed clustered computing applications at the InterOp trade show in early May.

Sun announced its SparcStorage Array subsystem in late March, the first complete Fibre Channel product to hit the market. This compact (8.9- by 19.5- by 21-inch) mechanism can attach up to 30 disk drives to a single I/O port. The cabinet contains three racks, each holding up to 10 535-MB fast SCSI-2 or 1.05-GB fast/wide SCSI-2 disks. Current maximum c apacity of the unit is 30 GB. The drives all use a special single connector that simplifies connection to the array.

The SparcStorage Array supports RAID levels 0, 1, or 5 at the low cost of about $1.65 per megabyte. This economy is possible because the array logic uses CMOS-like technology, which is considerably less expensive than other alternatives, such as GaAs (gallium arsenide). However, CMOS can't operate at 1 Gbps, so components for that higher speed will be expensive.

The array comes with the SparcStorage Volume Manager, which provides on-line data administration and configuration. The Volume Manager uses the same GUI as other Sun Solaris products, and it allows a full range of configuration operations even while the system is on-line. Pricing for the SparcStorage Array ranges from $24,900 for a 6.3-GB unit to $50,900 for the fully loaded 31.5-GB configuration.

To support the high data rates that Fibre Channel delivers, Seagate is implementing a serial hard drive interface. This will be a serial SCSI implementation allowing 106 MBps across the interface. To maximize performance and minimize cost, Seagate will implement only a subset of the Fibre Channel features. Its drives will be dual-ported and support port bypass for reasons of reliability and performance. That is, while each drive can only transmit data to a single port at a time, commands will be able to bypass a busy device and go on to the next address.

Although data transfer rates are currently in the 6-MBps range, areal densities are increasing and should double by 1996. Jim Coomes, a senior engineer for Seagate, says, ``Our computer modeling and simulation systems indicate that with 64-KB transfers and 16 devices, we should be able to achieve just over 90 MBps out of an arbitrated loop or string of drives.'' Seagate's first Fibre Channel product will join its 4-GB ``Barracuda'' family of drives. The goal is to produce these drives at the same price point as their fast/wide differential SCSI siblings. Sample units sh ould be available by September, with production scheduled for the end of the year.

Besides its speed, one of the best features of the Fibre Channel standard is the modularity and interchangeability of its components. According to Bryan Yunker, engineering specialist for Eldec, ``Fibre Channel is not just for disk drives or even storage products, but instead, it is extremely adaptable, lending itself to a wide variety of LAN applications.'' Originally an aerospace company, Eldec began producing Fibre Channel components a couple of years ago; they manufacture the physical interface for SparcStorage. At present, Eldec products use Triquint chips.

HP's initial offering will be an as-yet-unnamed switch with four slots supporting up to 16 card-mounted ports. Each card can have four 266-Mbps ports, two 532-Mbps ports, or a single 1-Gbps port; users will be able to mix and match cards according to their requirements. Announced in May, the product is due by year-end.

The HP switch will feature spe ed matching in Class 2 and Class 3 connections, tuned to the requirements of the connected port. Ed Frymoyer, HP's program manager for the Fibre Channel Systems Initiative, says, ``The first iteration of the product will have communications based on the GLM (Gigabit Link Module), which will be powered by shortwave CD laser over fiber-optic cable, but the card connectors have a modular design, so customers will be able to use copper as it becomes available.'' Even with Class 2 operation, latency will be less than 10 microseconds, the best currently available.

At the May InterOp, HP also demonstrated a similar product, available from Ancor Communications (Minnetonka, MN), supporting its 700-series workstations in a clustered computing application. When available, the switch will connect to workstations via ``Lighthouse'' interface cards, which are EISA-bus Fibre Channel boards also made by Ancor. The target price of the HP switch is approximately $1500 to $1600 per port/connector.

HP is also worki ng on Tachyon, a chip-level product that will perform SCSI-to-Fibre-Channel and TCP/IP-to-Fibre-Channel transitions using Class 1 or Class 2 type connections at speeds of up to 1 Gbps. Vendors will be able to use Tachyon, some glue logic, and modular connector units to create Fibre Channel host adapters with low chip counts.

Besides creating OEM products for HP, Ancor is also an OEM partner with IBM, which used Ancor cards and switches in its RS/6000 Fibre Channel demonstration at InterOp. Like the other major vendors in this market, IBM is concentrating its early efforts on midrange and workstation computers, presumably because users of these systems can best afford the costs of early release hardware.

What's Next?

The Fibre Channel Association plans more than just I/O and clustering products. According to Eldec's Yunker, ``the proliferation of Fibre Channel is going to be gated by the cost per port of connection, and despite its performance advantage, it will have to be priced competitively with more established technologies. It is the responsibility of the early hardware providers to ensure that goal is achieved.''

One of those technologies is ATM (asynchronous transfer mode). (See ``All-Terrain Networking,'' August 1993 BYTE.) Fibre Channel and ATM are not competing technologies. Instead, they are complementary. ATM will provide the network bandwidth required, but it won't offer the error correction and guaranteed delivery of Fibre Channel. Also, ATM's small frame size (53 bytes) means prohibitive overhead for some applications. What ATM can provide is high-speed, long-distance connections and a substantially lower connection cost. MicroAccess (Fremont, CA) will deliver a sub-$500 ATM interface card this summer.

Right now, disk access is driving Fibre Channel implementations. But an important future consideration is that PCI and other local-bus systems have high-frequency loading, which limits the number of slots. System designers will need multiport I/O, something Fibre Channel provides. With Fibre Channel, you can have an Internet Protocol connection, multichannel disk and storage peripheral access, a link to an ATM switch, and more--all from the same host adapter card.

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John Bryan is a freelance technology writer and consultant based in San Jose, California. You can reach him on the Internet or BIX at editors@bix.com .