@gamera,

With any router, I imagine that 16TB will be a tall task. I wasn't able to find a hard set limit, but I will keep looking. However, my team made me aware that the limit was raised to 8TB for some devices, but it depends on the model. 

For 16TB of data, I would recommend looking at some sort of network attached storage. I would imagine that the router having to keep track of that much metadata and files names could potentially bog the router down. I would also be willing to bet that the router is keeping your drive active and online so that it can be seen on the network. While this isn't as much of an issue for small disks because of how inexpensive they are, it does put additional wear and tear on your drive. This is also dependent on if it is an HDD or SDD drive.

Also you do not need to format the drive before adding it to the router, you can easily move files to and from the drive after setup