Fibre Channel Enters 2Gbit On-Ramp.

The growing demand for data storage bandwidth can be compared to the utilization of speed limits on the nation's highways. When the speed limit was 55 miles per hour, people traveled at that speed. When the speed limit was changed to 65 miles per hour on some highways, most people immediately moved up to traveling at that speed.

The same is true for the utilization of the bandwidth required for data storage and transfer. As bandwidth I/O becomes more readily available, users quickly maximize it and then begin to demand more. Fibre Channel-based storage is no exception. As users implement Fibre Channel in storage networks, they are discovering the need for even greater speeds in data transfer. The highway is being paved for the next evolution of Fibre Channel that provides data transfer at speeds of up to 2 gigabits per second (Gbps).

Fibre Channel is a high-speed data transfer interface technology that enables I/O and networking functionality to be merged through a single, high-speed connectivity technology. Devices within a network-servers, data storage systems, and peripherals-can communicate concurrently using common transport protocols such as IP and SCSI. Fibre Channel is unique in its ability to provide interoperability among multiple topologies, including point-to-point, arbitrated loop, and switched.

The proliferation of the Internet as an everyday tool for consumers and corporations alike and the increasing utilization of multimedia capabilities have fueled explosive demand for very large bandwidth. The increased demand for bandwidth in communications processing, however, created bottlenecks not only in the communications network, but also in critical peripheral functions such as data storage. Fibre Channel subsequently developed as a standard to address the data storage bandwidth and performance issues that emerged from the explosion in dataintensive applications.

The first generation of Fibre Channel enables connectivity among devices at speeds of up to 1Gbps. Users, however, can quickly maximize the capabilities of lGbit Fibre Channel, particularly in loops supporting a large number of devices. Subsequently, the next evolution of Fibre Channel is emerging. This generation of Fibre Channel provides simultaneous transmit and receive operations yielding up to 400MB/sec throughput in dual loop configurations, doubling the fundamental frequency of data transfer to 2Gbps.

The exponential advances made over the past few years in the storage capacity of disk drives has greatly influenced the advent of 2Gbit interface speeds. The disk drive industry has been able to virtually double the storage capacity of a single disk drive about every year-and-a-half. Since there is a correlation between raw disk transfer speeds and the speed of the supporting data transfer interface, these increases in storage capacity are related to parallel improvements in data transfer rates.

The increased rotational speed of today's disk drives, coupled with high areal density, has resulted in raw disk transfer rates becoming ever closer to the interface speed. It is this increased speed that has prompted 2Gbit Fibre Channel to emerge as a reality. When multiple drives are striped across the interface, the saturation threshold is reached much earlier.

This situation is similar to the development of SCSI, where the transition has gone from five megabytes per second to 160MB/sec utilizing a geometric progression. Initial disks, which were capable of transferring data at 1MB/sec, were adequately supported by the initial 5MB/sec SCSI-1 interface.

The speed of 2Gbit Fibre Channel is particularly beneficial to applications where high sequential bandwidth is required such as Internet applications, video editing, and medical imaging. These applications require the storage and transfer of enormous amounts of data, often in a single file and often in realtime. For delay-sensitive applications such as media broadcasting interruptions of even milliseconds in the transfer of data can be detrimental, causing severe disruptions in the data transfer process. Transferring data at speeds of 2Gbps ensures that the transaction occurs quickly and reduces the possibility of interruption during data transfer.

As an enabling technology for Storage Area Networks (SANs), 2Gbit Fibre Channel also is important to enabling SAN deployments where many directly attached servers must talk via the network. As the number of devices in a single loop increases, the need for arbitration among these devices during a data transfer increases.

Fibre Channel arbitrated loop can support up to 126 devices within a single loop. However, multiple transfers of large amounts of data occurring from several devices simultaneously can quickly cause saturation of the network. In current Fibre Channel arbitrated loop, this saturation can occur at a device count of seven or less. 2Gbit Fibre Channel enables double the rate of arbitration and data transfer, so a device can transfer the data and get off the loop faster. As a result, the potential for network saturation is reduced and overall network performance is improved.

Gigabit solutions are in place today and the adoption of 2Gbit Fibre Channel is on the horizon. During the second half of 1999, several vendors successfully demonstrated 2Gbit Fibre Channel capability at shows such as Fall Comdex '99 and several major vendors, including disk drive suppliers, storage systems providers, and host bus adapter providers, either announced 2Gbit Fibre Channel-enabled products or communicated plans to support the standard by the end of 2000.

Increasing data transfer speeds to 2Gbits is not without its challenges, however. Backward compatibility, increased power consumption, and an increase in RF emissions are all factors, which must be considered when designing 2Gbit Fibre Channel-enabled components and systems. Many vendors are working to resolve these issues with products likely to appear on the market by the middle of this year.

The issue of interoperability also continues to challenge vendors of data storage systems and components. Full compliance to the Fibre Channel standard is not yet available because many vendors still have proprietary elements to their Fibre Channel-enabled products. Ongoing interoperability plugfests demonstrate how vendors are working in close cooperation to promote full interoperability of the Fibre Channel standard and move it on to the next generation.

Today's data explosion presents unprecedented challenges for storing and transferring data. The evolution of Fibre Channel creates a new dynamic for speed and connectivity that will not only enable existing applications to run faster and more reliably, but will also open the information highway to a whole new set of possibilities.

Alan Johnson is the manager of emerging technologies at Eurologic Systems (Dublin, Ireland).