Using an earlier version fo the ReadyNAS formware, I previously formatted a Seagate ST4000VN000 4TB NAS drive to it's 4TB capacity, and used it as an external backup drive. I got an error after using it recently, so I tried to reformat the drive using the ReadyNAS GUI, and I could only get it to yield 2TB of capacity after formatting it in either EXT3, EXT4, or BTRFS.
Interestingly, I plugged the drive into a MacOS 10.11 system, and was able to format it to 4TB, run Disk First Aid, and found no errors.
After formatting it on the Mac, I plugged-it back into the ReadyNAS (with 6.6.1 firmware), and saw that it was formatted with Mac-HFS with a capacity of 3.67TB. After reformatting it to BTRFS on the ReadyNAS, I still saw 4TB (well, 3.64TB, actually).
So I'm not sure if the is a bug with the ReadyNAS 6.6.1 firmware, but it seems to be. Formatting a drive attached to the ReadyNAS should yield it's full cpacity, and render it logically (if not physically) erased.
