What type of HDD's do the Duo 4TB ship with?

I cannot seem to find any inof on the model of drives inside the box

They are WD Green 2TB drives.

WD20EARX or WD20EZRX most likely.

Tony, when it is practical, will I be able to buy and use the new red drives in the MBLD?

Thanks,

Bill

I have no idea. 

http://community.wdc.com/t5/My-Book-Live-Duo/WD-Red-on-My-Book-Live-Duo/td-p/434722

I think I found an answer:  an upgrade to the new Red HDDs is not currently possible.  The firmware will not support them in thje current MBLD.  In the future all WD devices will be using the Red drives.

Thanks,

Tony