If you mean putting a 3TB SATA into a USB dock, you need to:
1. Make sure your USB dock supports > 2TB - USB 2.0 ones do not, and early USB 3.0 docks do not either.
2. Put the SATA HDD into the USB dock first
3. Format by Magic TV
If Windows 7 cannot format the 3TB properly when using your USB dock, it does not support > 2TB.