General :: Copy Files With Preserving The Attributes?

I need to copy my data from the pc to an external hard drive with keeping the attributes; so i used the command

cp -rp ~/sourceDir ~/Destination

but when i am coping it it give the error message "cp: failde to preserve ownership for 'file' : Operation not permitted and it copied the files to the destination but the attributes has changed from

-rw-r--r-- to
-rwxr-xr-x

I tried to copy it by loging as the root also but still the same thing happens. how to copy the files with preserving the attributes