to-server and server-to-storage connections for Wintel machines. By 2000, they hope it will be common even on Pentium II machines.
Fibre Channel vendors point to the speed, distance, scalability, and flexibility of their technology. The table
"Comparing Fibre Channel"
compares Fibre Channel with other technologies. The comparison with SCSI is critical, because most Fibre Channel vendors now see their initial opportunity in the storage arena, where SCSI is the main competitor.
In addition, Fibre Channel is always hot-pluggable. Devices adhering to the current SCSI standard are hot-pluggable only via proprietary methods.
Fibre Channel's raw bandwidth is a little over 1 Gbps. If you take off 20 percent for overhead, you get
800 Mbps (or 100 MBps). Full-duplex (dual-ported), that's 200 MBps.
Fibre Channel has plenty of growth potential, too. We could see 10-Gbps Fibre Channel in coming years.
Released products have not yet achieved Fibre Channel's theoretical distance limit of 10 kilometers without extenders or repeaters. Early products were often limited to 500 meters. Today's products may go up to 2 km. However, 10 km will come eventually.
SCSI is unsuited to long distances, because of the fat cables (50 to 68 wires) necessitated by its parallel architecture. Fibre Channel requires only two wires. That becomes more important as distances increase.
In addition, clocking -- deciding where one bit ends and the next starts -- is easier with serial technologies, where you don't have to coordinate multiple lines.
Fibre Channel can consistently achieve 30 meters with coaxial cable. Twisted-pair Fibre Channel products, such as the FibreNet line of cards and disk arrays from Transoft (Santa Barbara, CA), ca
n support runs of up to 65 feet.
You'll probably never see a Fibre Channel loop with 127 devices on it. However, dozens of storage devices on a loop are reasonable. Switched Fibre Channel can support 16 million devices per switch theoretically, hundreds realistically.
In addition, Fibre Channel lets multiple servers share multiple storage devices. In contrast, SCSI's design assumes one server per storage device, and it's hard to go beyond two servers.
Fibre Channel's support for the major peripheral command interfaces, including SCSI-3, High Performance Parallel Interface (HIPPI), and Intelligent Peripheral Interface (IPI-3), provides support for various types of peripherals using just one server adapter card.
A single Fibre Channel-based Storage Area Network (SAN) can connect peripherals to servers and servers to servers.
"Our Fibre Channel customers like the fact that they have only one interface to worry about now, only one training to do, one vendor to deal with," says Marc F
riedmann, president of Prisa Networks (San Diego, CA), a network solutions provider specializing in the entertainment industry.
Fibre Channel also supports
three architectures
: point-to-point, Fibre Channel Loop (FCL), and switched. FCL offers low cost and the convenience of daisy chaining devices, but it suffers from the performance limitations of a shared medium. Switching offers more fault tolerance (because switches can isolate malfunctioning devices) and higher performance. In contrast, SCSI's bus architecture limits designers to the shared-medium approach.
"When I explain [to clients] what they get with Fibre Channel, their eyes light up," says Anders Lofgren, an analyst specializing in storage with the Giga Information Group, a market research and consulting firm based in Cambridge, Massachusetts.
"In some cases, it's because of the performance, in others the distance, and in still others the number of devices they can get on a loop," Lofgren says.
"There's
nothing else that can handle the combination of storage and network as well as Fibre Channel," says Friedmann. "We are hearing a lot about Gigabit Ethernet. But it doesn't talk directly to storage, and it's half the speed of Fibre Channel. More important, Ethernet is about four times the processor load."
On the Other Hand
However, not everyone has both feet firmly planted on the Fibre Channel bandwagon. In fact, moderates, fence sitters, and outright skeptics abound. They argue that Fibre Channel is immature and does not integrate well with legacy equipment, and that SCSI and Ethernet fulfill most needs.
"Our customers are not saying they absolutely have to have Fibre Channel today," says Dave Richardson, who is the director of business development for Berkshire Computing, an integrator based in Hopkinton, Massachusetts. "They're mainly looking to make sure their investments are protected. The partners we work with, like Digital Equipment, have a strategy that will let our customers upgr
ade to Fibre Channel when it's ready."
"Today, there are too many incompatibilities between Fibre Channel products from different vendors, and Fibre Channel is not robust enough for most production environments," says Berkshire's Richardson.
Living with the Legacy
With Ultra-SCSI-2 coming in at 80 MBps, and Ultra-SCSI-3 on the horizon at 160 MBps, SCSI satisfies most users' performance needs today. A single microcomputer today normally can't even max out an Ultra-SCSI interface, much less Fibre Channel. Microcomputers with 64-bit PCI buses, which are due out this year, can take much better advantage of Fibre Channel.
SCSI will make it much more difficult for Fibre Channel vendors to get into the mainstream market and achieve the economies of scale they need to compete on price.
Another big problem with Fibre Channel is its lack of integration with legacy storage devices and networks, notes Kon Leong, president of GigaLabs, which is a manufacturer of Ethernet switches. For inst
ance, there is no Fibre Channel-to-Ethernet bridge, and you need a SCSI-to-Fibre Channel bridge to use current SCSI devices on a Fibre Channel network.
Ethernet Rules Networks
For server-to-server connections, Fibre Channel also faces formidable competition. For instance, Carl Howe, director of network strategies with Forrester Research (Cambridge, MA), a consulting and market research firm, thinks Gigabit Ethernet could become the standard for all but the most demanding server-to-server applications, where people want all the performance they can get "and don't care what it costs."
One approach to the problem of TCP/IP processing load is the Intelligent I/O (I
2
O) specification, championed by the I
2
O special-interest group (SIG) and Intel. I
2
O can speed up I/O processing substantially by using a separate I/O processor to handle real-time functions. Downloadable software upgrades to IP might improve speed.
Another approach is to move TCP/IP functions
into switch hardware. Rapid City Communications (acquired by Bay Networks in June 1997) has done that in its F1200 Gigabit Ethernet routing switch that performs IP route computation at switch-like speeds. Similarly, Cisco's Netflow LAN-switching technology, implemented, for instance, in Cisco's 5500 Ethernet switch, achieves near wire speeds with TCP/IP traffic.
ServerNet and SCI
Another option for high-speed clustering is ServerNet, from Tandem/Compaq, a full-duplex 40-Mbps interconnect optimized for clustering. Compaq has committed to making ServerNet the standard for Windows NT-based clusters. Even though ServerNet is not an official standard, Intel, Microsoft, Oracle, and Informix have all pledged support. Microsoft includes ServerNet drivers with the Microsoft Cluster Server (MCS, formerly code-named Wolfpack).
There are other players, as well. One of these is the scalable coherent interface (SCI), from Dolphin Interconnect Solutions. SCI now offers speeds of 500 MBps (1 GBps bidirec
tional) and low latencies that are valuable for supporting transaction-oriented applications such as databases. Where SCI achieves a latency of 2 microseconds, FCL might take 20 µs.
Yes, But...
Each of the alternatives to Fibre Channel has weaknesses. SCSI's technical drawbacks are discussed above.
Ethernet may be 30 percent to 50 percent less efficient than Fibre Channel for typical server-to-server applications, says Forrester's Howe. In addition, Fibre Channel provides error handling in the chip. Ethernet doesn't, so you need a software stack, such as TCP/IP, that does. That means high latencies.
Furthermore, three years from now, Ethernet chips and Fibre Channel chips will cost about the same for comparable speeds, predicts Ed Frymoyer, president of EMF Associates (Half Moon Bay, CA), a consultancy specializing in Fibre Channel. On a cost-per-Mbps basis, Fibre Channel is already less expensive than Gigabit Ethernet today, he adds. Frymoyer also says that he expects three Fi
bre Channel-to-Ethernet bridges within a year.
As for SCI, it is a parallel technology, limited to one data center. A serial version, planned for 1999, should greatly increase distances and lower costs. By that time, though, Fibre Channel may be too firmly entrenched, consigning SCI to a niche role. In addition, switched Fibre Channel may have hardware latencies comparable to those of SCI.
Step by Step
Lofgren sees three stages of Fibre Channel adoption: SCSI replacement (starting now); single-vendor, multiserver sites (this year); and multivendor sites (1999). The major opportunity lies in phase three. Until that happens, direct sales may predominate.
"Customers need to evaluate Fibre Channel before buying it," says
Michael Dolan
, national sales manager with AVDigital (a subsidiary of North American Systems, Minneapolis, MN), an integrator that resells Prisa's products and specializes in the film, video, and postproduction industries. "Most of them are still i
n the evaluation phase."
"We're advising clients to buy from server vendors who are OEMing Fibre Channel," says Lofgren. "It's safer to go to systems vendors, because they guarantee the management capability."
Nevertheless, even today, customers want to be talking to an integrator with expertise in Fibre Channel, Dolan says.
Integrators
will come to play more of a role as multivendor installations become more common. Vendors are working at remedying interoperability problems and testing the results at venues such as Networld+Interop. For instance, at last October's Networld+Interop in Atlanta, switch manufacturers such as Ancor, Brocade, and McData; adapter manufacturers such as Interphase and Jaycor; and storage vendors such as Ciprico all made announcements proclaiming Fibre Channel interoperability.
Fibre Channel U
Salespeople must look for opportunities to take advantage of Fibre Channel's edges over SCSI. One of these is its superior disaster recove
ry by putting mirrored drives in different data centers.
Fibre Channel's speed, distance capabilities, flexibility, and scalability have earned it a secure niche at the high end of the peripheral market. As it further expands in that market and into the emerging server-to-server market, it is a significant opportunity for resellers who can help customers with evaluation and bulletproof implementations of Fibre Channel technology.
Where to Find
Ancor Communications
Minneapolis, MN
Phone: 612-932-4000
Internet: http://www.ancor.com
Swimming the Fibre Channel
