# creating two bytes long file
bash-2.05b$ echo 1 > test

# ls -l reports logical size of file
bash-2.05b$ ls -l test
-rw-r--r--    1 ilya     ilya            2 Jul 24 15:25 test

# du -b reports physical size of file
# (4096 - size of block on my filesystem)
bash-2.05b$ du -b test
4096    test