In the grub shell, specify the file file as the actual drive for a
bios drive drive. You can use this command to create a disk
image, and/or to fix the drives guessed by GRUB when GRUB fails to
determine them correctly, like this:
grub> device (fd0) /floppy-image
grub> device (hd0) /dev/sd0
This command can be used only in the grub shell (see Invoking the grub shell).