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Loving My Job

Don MacVittie replies: Ron, you might be pleased with one of the higher-end ($40,000-$100,000) iSCSI SANs, but if you can wait, I would recommend getting iSCSI on 10-Gigabit Ethernet when it becomes readily available next year.

NAS involves file-level interaction: You request a file, and the NAS server reads it and serves it up. This is slower than the block-level interaction of SANs, where the computer on which you're running AutoCAD requests only the blocks it determines you need.

Fibre Channel and iSCSI use block-level interfaces. Hence, they're both suitable for CAD. Unfortunately, you have to pay a lot to get the throughput you need on an iSCSI SAN. The math for iSCSI is such that 10-Gig is almost mandatory for high-throughput functions. Because the network measures in bits and throughput measures in bytes, you must divide your network pipe by 8 to get the maximum byte throughput. That hurts.

The overhead from iSCSI can also be taxing in high-volume situations, where we've seen CPU usage spike by as much as 80 percent. Of course, iSCSI host bus adapters or TCP off-load engines can alleviate the problem; so can adding more Ethernet ports to the iSCSI SAN, as vendors like EqualLogic and Intransa do.

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