Fiber optics finds a place in SANs

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The storage and retrieval of digitally formatted information has ramped up rapidly over the past five years. More enterprises are sending more new data to storage on tapes and disks, while relatively little legacy data is deleted. Increased security concerns also are supporting the deployment of duplicate (mirrored) remote storage-area networks (RSANs). The need to access increasing amounts of data very quickly translates to a rapid increase in data rates of both SAN equipment and the transport trunk from SANs to other SANs or desktops. That in turn has driven conversion from copper interconnect to increasingly high-data-rate fiber-optic links.

There are three significant applications for fiber-optic signal links in SANs:

  • Intra-equipment—connections within servers, routers, switches, and other SAN/RSAN equipment).
  • Inter-equipment—connections within the SAN/RSAN between routers, servers, and other equipment).
  • RSAN and enterprise core SAN connection to external long-haul transport network nodes (regulated telecom central office or Internet point of presence or to other SANs).

The strong upward trend in data rates and parallel access/processing is driving an increase in the number of internal interconnect links and the data rate per link within SAN equipment. That supports the strong growth of multifiber transceivers and optical backplanes. Multifiber transceiver links have advanced steadily—from 10 Gbits/sec to 40 Gbits/sec, with 160 Gbits/sec now introductory and 2.56-Tbit/sec links forecasted by 2005.Th 107009

The global consumption of fiber-optic components in links within and between SAN equipment plus SAN-to-SAN trunks will grow steadily from a recession-retarded $142 million in 2001 to $1.32 billion in 2006. This growth will be dominated by transceivers (T/R pairs), with a 75-78% share across the forecast period (see Figure). Fiber-optic-cable assemblies also will hold a substantial market share: 17%, or $220 million, by 2006.

As fiber has displaced copper for inside-SAN equipment interconnect links, Fibre Channel has evolved as an industry-standard protocol. Meanwhile, Ethernet protocol has dominated enterprise internal interconnect (LAN/MAN), Internet access, and long-haul trunk applications. For various reasons, Ethernet holds a significant cost advantage over Fibre Channel per gigabit transported, and this advantage is increasing.

Ethernet protagonists are many, strongly organized, and cooperative, and they anticipate rapid displacement of Fibre Channel by Ethernet within SANs. Legacy position, however, is a powerful displacement-retarding factor, and Fibre Channel vendors are protecting their market. ElectroniCast forecasts a relatively gradual Ethernet penetration of SAN internal interconnect, reaching a 28% transceiver value share by 2006.

Major enterprises typically have two or more SANs and require very-high-data-rate transport among SANs. SANs, and their interconnections, are planned and implemented by system integrators (which also are leading SAN equipment vendors) such as IBM, EMC, Hewlett-Packard, and Brocade. Cisco Systems also is a leading equipment provider to SANs and SAN-to-SAN links.

Ethernet dominates here, as well. These between-SAN links typically are 10-Gigabit Ethernet per wavelength, singlemode. Up to 2,000 channels can be achieved by a combination of subcarrier modulation and DWDM, which typically moves over the unregulated fiber of national and international carriers. RSANs often require deployment of dedicated trunk fiber.

The internal interconnect data rate between boards and cards of servers and routers has increased rapidly over the past five years. This trend will continue. There are three basic choices for achieving higher data throughput between points in the equipment:

  • Higher data rate on a single serial channel—single fiber.
  • Multiple wavelengths on a single fiber (WDM).
  • Serial transmission on each of multiple parallel fibers.

There are also hybrid techniques. For long-haul, DWDM plus higher data rates per wavelength has proven-in as the optimum economic choice. Multifiber links can evolve to higher data rates per channel (and theoretically, WDM on each of multiple fibers). In practice, economics dictate the choice between alternatives.

For short- to medium-reach (1-1,000 m), multifiber transmit/receive modules have emerged as the winner. Thousands of internal interconnect multifiber links were used in servers and routers in 2000-01, and 40-Gbit/sec-throughput multifiber links are now commercially available. Over 90% of these links are less than 10 m in length. They are deployed within and between shelves and cabinet-to-cabinet. Multifiber links with 160-Gbit/sec throughput are available for evaluation and design-in.

ElectroniCast forecasts 2.56-Tbit/sec throughput multifiber links to be in evaluation in 2004. For throughput rates above 10 Gbits/sec and reach less than 10 km, multifiber links will be the economics-driven choice.

Multifiber-link module deliveries through 2001 were dominated by Infineon. Agilent Technologies and JDS Uniphase (through the latter's acquisition of IBM's optical link operation) are also major suppliers. Molex has developed an alternative-source capability to Infineon, and about a dozen other vendors are serious contenders.


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Jeff D. Montgomery is chairman and founder of ElectroniCast Corp. (San Mateo, CA), an optical technology market research and analysis firm.

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