Duo v2 Compatible USB 3.0 3TB and/or 4TB drives

Can we get a list of compatible 3TB and 4TB drives for the ReadyNas Duo v2? Are there any? Spent about an hour looking around here and I found one person saying they got it to work but only by manually formatting the drive themselves and partitioning it to 2TB and and 1TB. I just bought by device yesterday and was able to plug in two 3TB internal WD green drives in a raid one and it's working great so far. I'd like to get a 3TB external drive to use for backup but can't find any solid information.

thanks