dev=/dev/sdb1

# skip these many gigs between tests
skipfactor=20

diskbytes=`fdisk -l |grep "${dev}" |awk '{ print $4 }'`
diskbytes=`expr $diskbytes \* 1024`
maxgig=`expr $diskbytes \/ 1073741824`
maxgig=`expr $maxgig - 1`

echo "Maximum offset ${maxgig}GB"
echo "-------------------------"

for q in Read Write; do 
    echo "=== $q: ==="
    offset=0
    while [ $offset -lt $maxgig ]; do
        if [ "$q" == "Read" ]; then
            rate=`dd iflag=direct if=${dev} bs=1G skip=${offset} count=1 of=/dev/null 2>&1 |grep seconds |awk '{ print $8" "$9 }'`
        else
            rate=`dd oflag=direct if=/dev/zero bs=1G seek=${offset} count=1 of=${dev} 2>&1 |grep seconds |awk '{ print $8" "$9 }'`
        fi
        echo "Offset ${offset}GB: $rate"
        offset=`expr $offset + $skipfactor`
    done
done