[CentOS] accurate file size

[centos at unixplanet.biz]

Hello

I was copying some files from one server to other,
that I relized the total file size ( sum of all files )
in one server is a bit more than the one that copied from
( about 6 when I do du -s )

individual file sizes are identical, when I do one by one file
comparison, but the sum is different.

is there any more accurate way to make sure of integrity of the file.
( other than pgp or signature )

Thanks