Biggest I have had work on a I-series was 14TB reliably. DS-7616NI-I2. Larger hard drives either wouldn't format and give an error which in turn shows an "abnormal" status for the drive Also have a DS-7732NI-M4. I've got two 18TB's running so I know that would work. I tried a setup with four 18TB's and it worked also. I didn't have any hard drives that are bigger on hand so wasn't able to try them.
