It will only scan the entire disk if you're using Linux... as you can pass a "device" name to the keyhunter.py script in Linux and keyhunter.py will attempt to treat it like a "file" and start reading through it.

Linux: ./keyhunter.py /dev/sdc

/dev/sdc is a "device" like a harddisk... EDIT: unfortunately, you can't do this in Windows. It doesn't work that way. So, you'd need to create an image file of your disk using some sort of disk imaging tool and then pass that image file to the script.

For windows you need to use \\.\PhysicalDiskN where N is the number of the disk you are trying to read (Credit to 2112):

Otherwise, your best bet is to forget about keyhunter... and use pywallet. It has a recover mode for scanning whole disks/images.