Hey again.
Are you sure that this drive is working properly. Not being able to run the test on it might mean that the drive is faulty. I don't think it's a problem with the drive's capacity.
I recommend that you test the drive with one of the diagnostic tools from the article I've posted in one of the previous threads. (Here it is again so that you don't have to look for the other thread: https://www.lifewire.com/free-hard-drive-testing-programs-2626183).
Let me know how it goes.
Boogieman_WD