Q

Real performance issues

I see a great discussion and a wide range of opinion about iSCSI vs. FC but I couldn't find any information about real performance. Does a Gbit Ethernet link perform in the same way as a 100MB/sec FC? Are they efficient in the same way?

Remember iSCSI is mostly a pipe dream today but products are coming. The biggest differences between FC and iSCSI are in latency. High throughout transaction processing systems will need FC because FC switches have much better latency characteristics than Gigabit Ethernet switches. I believe FC HBAs are also more efficient than Gigabit Ethernet NICs when it comes processing their respective protocol stacks.

As to flow control, Gigabit Ethernet has the PAUSE control which effectively throttles sending nodes (unlike previous versions of Ethernet), FC has link credits. A complete analysis needs to be done but I think these two methods will be roughly equivalent in terms of network efficiency. My OPINION is that Gigabit Ethernet's PAUSE method will be more efficient because it is less complicated and is only invoked when needed.

iSCSI vendors are working on TCP offload technology to move the burden of TCP algorithm processing from host processors to adapters. Once that problem is solved sufficiently, there are going to be many applications where iSCSI will work just as well as FC.

Regards,
Marc Farley

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This was first published in October 2001

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