$ dd bs=4k count=655360 if=/path/to/copy/on/disk/1/file | wc -l &
$ dd bs=4k skip=655360 count=655360 if=/path/to/copy/on/disk/2/file | wc -l &
$ dd bs=4k skip=1310720 count=655360 if=/path/to/copy/on/disk/3/file | wc -l &
$ dd bs=4k skip=1966080 if=/path/to/copy/on/disk/4/file | wc -l &

python -c "print len(open('test.txt').read().split('n'))"

bash-3.2$ sed -n '$=' test.txt
519

bash-3.2$ python -c "print len(open('test.txt').read().split('n'))"
519