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About the only advantage CalDigit's RAID card has over the competition is that like the Apple card, it has chip-level support for the 2009-10 MP's internal SATA backplane.

Beyond that, it's not a particularly good RAID card. Its external array support is locked down to their proprietary HD Elements boxes, which I would imagine continue to be cheap Hitachi consumer drives dressed up in fancy clothes.

Despite having to use modified drive sleds for the internals, you'll get a lot more functionality (and perhaps better reliability) in the end with something from Areca or Atto. Nanofrog is the resident expert here on RAID configurations though, so he would be the best guy to ask.
 
I picked up a 2009 Mac Pro, upgraded the firmware to the 2010 firmware, upgraded the CPU to the 3.2Ghz 6-core, upgraded the RAM to 32GB, installed a bunch of hard drives and I spent about $2500 total after I sell my existing CPU. No warranty, but I think it is a good option and will hold its value in the long run.
 
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