I just wanted to give everyone a heads up that my 8TB HDD is connected to my Roku Ultra using a USB 2.0 cable extension. The cable has a right angle attachment to keep the media area more organized. I'm using the Roku Media Player app and my .mkv and .mp4 files are playing great. **Note - It took over 4 minutes for the Roku to recognize the 8TB Seagate USB 3.0 HDD.** Once the HDD is powered up and connected to the Roku just wait, it will take time.
I also tested a 3TB Internal HDD using a SATA Docking station with a USB 2.0 connection and it also worked, and was recognized much faster than the 8TB.