Have you tried just tohd=/dev/sda4 to let Knoppix copy the DVD image over to HDD via itself
(hmmm..I forget if either "Knoppix" needs to be in the command or not -- ala >> "Knoppix tohd=/dev/sda4" )

Once done, then use fromhd=/dev/sda4

Is this an SCSI drive or External USB key or USB drive or SATA drive?