How was the drive formatted for NTFS? Did it come out of the box that way? If not how was it formatted using what OS or software?
It appears the v4.x My Cloud firmware has trouble properly mounting certain USB drives. There are several prior threads discussing the issue with no real solution. What worked in my case with one USB drive that wasn’t properly mounted by the My Cloud was to delete the USB drive’s partitions, then repartition the USB drive then reformat the drive for NTFS. I performed this via Windows 7 and was able to get the My Cloud to properly mount the USB drive. One can read my experience in the following thread which includes log detail:
https://community.wd.com/t/this-is-absolutely-unacceptable/149432
