Why is /public/_wdprot taking up 1.2T in 2TB drive?

I have a WDEX2, a 2TB drive with RAID configuration. My actual data size is less than ~400G.
But the size of share /public is ~1.2T. Why is that? What does it contain? what can i do to maximize the use of storage space on this drive? i am not and do not intend to use cloud.

Where is the used space displayed as 1.2TB? In Windows Explorer? In the unit’s Dashboard? In WD SmartWare? What happens if you try to enable hidden files and folders in Windows Explorer in order to confirm if there are additional invisible files stored within your unit?

Tracer, thanks for your response. 1.2TB shows on my dashboard. I am sure no one has wrote to /public because it is not mapped on any PC.

Windows keep showing the drive getting full.
This does not make sense. I have not tried enabling hidden files, I will try that on Monday.