Well, we were (and are) using a networked 10GbE RAID for footage….however from memory the 3 x 1TB SATA RAID got about the same throughput as our network (250mbps roughly)
This is enough to capture 1080 uncompressed 10bit QTs through a decklink. Will also let you edit a couple of streams of this. R3D 4k also good for editing with – but I suspect alot of the work being done to run that is from my Quadro card using OpenCL. This is an important addition for PPro these days. You are limited on options with the 2008 (3,1) Mac Pro, but Quadro 4000 runs fine on mine. Cheaper alternative is the GTX680.
EDIT: The SATA SSD scratch I have now is actually about 270MB r/w not 450+!….I was getting mixed up with a new Mac Pro we are testing at the moment, which is getting an insane 750MB+ from the internal Flash SSD!
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Adobe CC 2014
MacPro 3,1 8-core 3.2GHz / 32GB RAM / NVidia Quadro 4000 / OSX 10.8.5
Decklink Extreme+ 3D / 1TB SSD scratch / 6TB XServe + UD RAID on 10GbE