rsync: different target size

[Leonardo Canducci <leonardo.canducci@gmail.com>]

I'm using rsync -aHS to backup some stuff (mostly jpgs and docs from
my home) to an external usb hard drive (same ext3 fs).
After a backup I ran du -s to get a fast check on size and found
source and target to be slightly different.
Even using du -cb or du-cbk size doesn't match. So what's wrong?!

I've noticed some dir size doesn't match:
leo@zazzero:~$ ls -ld /media/toshiba-docs/foto/d50/
drwxr-xr-x 43 leo leo 4096  6 gen 11:17 /media/toshiba-docs/foto/d50/
leo@zazzero:~$ ls -ld /share/foto/d50/
drwxr-xr-x 43 leo leo 69632  6 gen 11:17 /share/foto/d50/

I'd like the size of the backup to be exactly the same and check sync
result with du.

BTW, is there some better fast check I could do to test rsync behavior?

Thanks!
-- 
Leonardo Canducci