<simple-scsi-disk>.save-diff-file filename [-overwrite]
Writes changes to the image as a diff file filename in the craff file format.
The command will fail if the destination file already exists, unless -overwrite is specified.
This is basically the same command as save-diff-file.
simple-scsi-disk
<simple-scsi-disk>.add-diff-file,
<image>.save-diff-file