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FireWire 800 throughput

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I am copying data from one external HD to another via FW800. They are daisy chained together like so:

MacbookPro =---= LaCie =---= iomega.

Because my 1st gen Mac only had FW400, I connect them through a FW800 ExpressCard.


According to Wikipedia, "FireWire 800 ... and corresponding products allow a transfer rate of 786.432 Mbit/s full-duplex" (98 MB/s). Both these external HD's are dual-disk 7,200 rpm RAID0 configurations. The LaCie Big Disk Extreme (16MB buffer) features boast "Burst transfer rate up to 80-90MB/s in FireWire 800". Macworld reviews of the Iomega Mac Companion (8MB buffer) report rates up to 79.6 MB/s. Am I correct in assuming the limiting factor in throughput speed is the drives themselves which aren't able to saturate the interface?


I used iStat Menus to monitor the HD activity and the peak read/write speed is 22.50 MB/s. Is it because they're daisy chained? Would I be better off with one HD plugged into the ExpressCard and one to a native FW400 port on my Macbook? Can anyone shed some light on as to why my files only transfer at a quarter of the full rate?


Cheers. ;)

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