Analysis: 4G Fibre Channel doubles speeds of SANs

The 4G bit/sec Fibre Channel standard boosts the performance of storage-area networks by doubling speed while maintaining backward-compatibility with 1G and 2G bit/sec systems. In addition, 4G bit/sec storage hardware will be available later this year at a cost comparable to today's 2G bit/sec products.

A task group at the Accredited Standards Committee developed the 4G bit/sec Fibre Channel link specifications for backplane connection between disk drives and drive controllers in storage arrays. ANSI approved the specification in 2002 as Fibre Channel-Physical Interfaces (FC-PI). Last May, the Fibre Channel Industry Association recommended 4G bit/sec Fibre Channel for switched fabric networks that connect these storage arrays to servers in the corporate data center.

SANs deployed today run at 1G and 2G bit/sec. As IT managers deal with an ever-increasing deluge of data from emerging bandwidth-intensive graphics and video applications, and new document retention and security requirements, they will need to increase Fibre Channel SAN capacity without increasing costs.

This can be accomplished by consolidating applications and data on a limited number of more-powerful servers and higher-capacity storage arrays, letting systems do more work without increasing the number of equipment racks that must be managed. This consolidation creates the need to move to higher speeds.

Using Fibre Channel operating at 4G bit/sec to connect disk drives to drive controllers allows increased speed while maintaining compatibility with existing gear. It also supports loop architectures common in 1G and 2G bit/sec systems.

Fibre Channel 4G bit/sec links in the network fabric are a good match with these new 4G bit/sec drive interconnects, because no encoding conversion is needed between the backplane and fabric.

At the server side of the network, fabric host bus adapters provide an interface between the server's internal data bus and the SAN fabric. The trend in server bus architectures is toward higher I/O bandwidth. Buses capable of 4G bit/sec throughput are available, and greater speeds are on the horizon.

To prevent bottlenecks and reduce latency, the speed of the SAN switch fabric must match disk and server I/O speeds. As more-powerful servers and larger disk arrays move to connection speeds of 4G bit/sec, 4G bit/sec fabrics will be necessary to handle the traffic between these devices.

Systems based on 4G bit/sec Fibre Channel will rate-adjust when connected to 1G and 2G bit/sec systems, letting IT managers make incremental network upgrades while using 1G and 2G bit/sec storage hardware. As the remaining infrastructure is upgraded, the full benefits of a 4G bit/sec system are realized.

Optical transceivers provide the interface between Fibre Channel systems and the optical fibers of the SAN. They represent a significant portion of the total cost of a SAN. Development of 4G bit/sec optical transceivers will not require a change in the semiconductor process technologies used to manufacture the internal components for 2G bit/sec versions, including lasers, laser drivers, PIN receiver diodes, trans-impedance amplifiers and post amplifiers. Therefore, once manufacturing is in full production, 4G bit/sec optical technology will be available at a price comparable to that of 2G bit/sec Fibre Channel hardware.

Demand for higher bandwidth, compatibility with installed hardware and comparable cost will lead to rapid and widespread adoption of 4G bit/sec Fibre Channel. It will replace 2G bit/sec in the same way 2G bit/sec replaced 1G bit/sec. By 2006, most Fibre Channel hardware will ship with 4G bit/sec interfaces.

- Zona is marketing director of the Enterprise Optical Modules Optical Platform Division of Intel.

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