Resume a dd operation with a check

_README.md

This little script resumes an interrupted dd copy at a given offset.

Before resuming, it rolls back (the amount of roll-back is OVERLAP_SIZE * CHUNK) then calculate the checksum of the overlap on both files to make sure that they are valid images of each other.

The checksums have to be checked manually by the operator (todo: automate).

mydd.sh

IDEV=$1;
ODEV=$2;
POS=$3;
LOG="/home/rolf/dd.log";
OVERLAP_SIZE=200
OVERLAP_POS=`expr $POS - $OVERLAP_SIZE`
CHUNK=95200

if [ $# -lt 3 ]
  then
    echo "Usage: mydd INPUT_DEVICE OUTPUT_DEVICE START_POSITION"
    echo "Example: mydd /dev/sdc /dev/sdb 840000"
    echo "Note: Needs super user"
    exit 0
fi


echo "Copy $IDEV -> $ODEV at $POS";
dd if=$IDEV count=$OVERLAP_SIZE bs=1MB skip=$OVERLAP_POS | md5sum;
dd if=$ODEV count=$OVERLAP_SIZE bs=1MB skip=$OVERLAP_POS | md5sum;
read -p "Please check matching checksums above then press Enter to continue";
echo "Starting at $POS" >> $LOG ;
dd if=$IDEV of=$ODEV count=$CHUNK bs=1MB skip=$POS seek=$POS conv=notrunc status=progress;
hdparm --idle-unload $IDEV;
echo "Please power cycle input device then launch this script again with adjusted parameters";