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You can get up to 10TB drives for around $720 right now:

http://www.amazon.com/Seagate-Enterprise-Capacity-200RPM-ST10000NM0016/dp/B01DAI6JUS?ie=UTF8&keywords=10tb hard drive&qid=1462821202&ref_=sr_1_5&sr=8-5

Or 8TB drives go for just over $200:

http://www.amazon.com/Seagate-Archi...qid=1462821259&sr=8-1&keywords=8TB+hard+drive

I'm using the 8TB of the above in my 5,1 with no problems.

I tried using the HGST 10TB drive (https://www.pcnation.com/web/detail...00-10-Tb-3-5-Inch-Internal-Hard-Drive-0F27452), and for some reason it won't spin up inside the 5,1 but will work on an external USB drive bay. Not sure if it's a matter of juice or what.
the HGST 10TB drives only work if you cover the leftmost 3 pins of the power connector with some non-conductive tape, or block them off with some other method.
 
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A little update as this drive was not on the list above and i tried it with success:
18TB version

Only 2 screws fit the tray, as the HDD has different holes.
Some 3m tape helped and placing it far to the right on my 2009 Mac Pro.

Hope this helps people, who are not sure about this drive and if the old boy can take it...
 
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