knoppix tohd=/dev/sda1 for example as an external usb hdd

outanet said that it will told knoppix to copy the cd image to /dev/sda1 and let knoppix running on the hdd and leave the cdrom/cdwriter free for other purpose

I have a question.
My usb hdd has some others data files, if I execute "knoppix tohd=/dev/sda1" wll it overwrite all existing files ? or will it partition the hdd ? which filesystem of the usb hdd should it be, fat32, ntfs, ext2 ?