drivesum

#!/bin/bash
# sha256sum each (megabyte-sized) block of /dev/sda, prepend the block number
# intent is to compare two drivesum lists and then dd out the changed blocks and send them to the other drive

device=/dev/sda
bs=1048576
size=$(blockdev --getsize64 $device)
sumsfile=/tmp/sums_$(date +%s).txt
blocks=$(( ($size+$bs-1)/$bs ))

#test: blocks=10

for ((i = 0; i < $blocks; i++)); do
  dd if=/$device bs=$bs skip=$i count=1 status=none | sha256sum
done | awk '{print n+0, $1; n++}'