Using 2 duo devices to backup each other?

I know that the duo device has raid options etc. But at the end we are talking about valuable files and since there’s no option to backup the device (both hdd) itself to another external hdd i wanted to buy a second duo device which i can use, Eg. taking the main hdd out of the duo and put it into my second duo for a mirror backup? so basically the second duo device would be used as second mirroring device this sound a bit awkward and expensive but WD has left no options for me…

please let me know if this is possible…

It is not possible to backup one MCH to another MCH.