I was wondering if there is any disadvantage if I use for farming for example an WD My Book Duo 12 TB, (external HDD). As far as I know the Duo are two drives put together?
It is slightly more risky since it is two devices smushed together pretending to be one device, and thus a bit more complex. I don’t think it’s a terrible risk but I wouldn’t recommend it if you can avoid it.
Chia is all about keeping it as simple as possible, no raid, no nas, no nothing, just simple directly connected disks with as little as possible between the disk and the operating system.