Start with the QNAP NAS HDD Compatibility list
- several 4 TB HDD listed already.
Pre-requirements: An out-of-the-box TS-112 might come flashed with older firmware, not able to partition a drive with a capacity exceeding 2 TB. The most simple way: If you have a spare HDD available (max. 2 TB), run a full initial installation with this HDD, and go for v3.7.3 (or the coming-up v3.8.1) firmware. Then your NAS box is ready to play the 4 TB drive. Enjoy!