in case of Seagate:
ST3000DM001 9YN166 3TB
ST2500DM001 9YN16L 2.5TB
ST2000DM001 9YN164 2TB
ST1000DM003 9YN162 1TBhttp://knowledge.seagate.com/articles/en_US/FAQ/223651en
I had to first update the firmware of the qnap nas, to see the hdd at all. then initialized and used the seagate hdd for some time, and then somehow after one restart there were problems...... for few months didnt solve it, and then... I updated the firmware of hdd!
I had ST3000DM001 with the firmware of CC4C and updated it to CC4H. So for now it resumed to work.
If I have to guess, this update can solve problems for many users, if it solved for you too, please respond about it.