Why does the computer's "disk management" include "unallocated" disk partition and why is the formatting of this partition unavailable after installation of a hard drive with a capacity exceeding 2TB on the TerraMaster DAS?

The source of the problem is the selection of the MBR partition for initialising the hard drive, as this can support a capacity no greater than 2TB. The GPT partition should be selected for hard drives larger than 2TB.