#!/bin/bash

d=hda
blocks_at_a_time=1000
readers=2

set -x
ds=`cat /sys/block/$d/size`
ds=$((ds/blocks_at_a_time))

for i in `seq 0 $((readers-1))`; do
	( while true; do dd if=/dev/$d of=/dev/null bs=$((512*blocks_at_a_time)) skip=$((ds/readers*i)) count=$((ds/readers)); done ) &
	pids="$pids $!"
done

trap "kill $pids; killall dd" EXIT

wait