Speed wars: Fibre Channel vs. Ethernet


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Cost and difficulty
Most managers will choose FC or IP based on other factors, such as cost and difficulty, not speed. Until now, IP was the undisputed low-cost champion, but the FC industry insists it's addressing the cost issue by cutting prices on some FC components, especially at the low end. "I've seen 2Gb/sec FC adapters priced at $345 retail," says Emulex's Scherer. That may be an improvement, but it remains higher than IP's $50 NIC card.

Before jumping on the 10Gb/sec Ethernet bandwagon because of price, add in the cost of a TOE to relieve the server of the overhead of processing the TCP/IP stack. At 1Gb/sec, a TOE isn't a factor because today's servers can absorb the overhead. "The rule of thumb is that it takes 1Hz of CPU to drive 1 bit per second," says Herman Chao, senior manager of product marketing in QLogic Corp.'s advanced technology and planning group. That translates into 1GHz of CPU to process a 1Gb/sec storage stream.

At 10Gb/sec, however, you'd need 10GHz of processing power. "For 10Gb/sec Ethernet to be viable for storage, you need a TOE," concludes Chao. This isn't an IP deal breaker, and Chao expects the cost of TOEs to come down as demand ramps up. The cost of the TOE still shouldn't be overlooked.

In terms of ease of use, IP and iSCSI hold the advantage over FC. Even a novice network admin knows IP, and iSCSI vendors have made great strides adding GUI interfaces to their products. The FC industry is working

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on the difficulty issue, says Tom Hammond-Doel, treasurer and membership chairman of the FCIA and director of technical marketing at Emulex Corp., but he couldn't cite specifics.

Disk bottleneck
End-to-end storage performance involves a number of components, including the communications link. Fast servers--and now fast links--will still be slowed by the disk array.

"Disk drives are a fundamental bottleneck," says Taneja. "Their ability to transfer data is already limited, and it will get worse as the pipes get bigger." Users can move to faster disk drives, but beyond 15,000 rpm, head vibration becomes a problem. Solving the disk bottleneck requires putting bigger buffers in front of the drives and using more drives in parallel.

Whether or not you're ready to take advantage of them, faster network links have arrived with even faster ones on the way. One technology isn't about to replace the other, at least in the foreseeable future. Companies will just have more options. Sun Health's Ronen, for instance, already knows what he'll pick.

This was first published in February 2006

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