a fast, versatile, remote (and local) file-copying tool
-a, --archive
       This is equivalent to -rlptgoD. It is a quick way  of  saying  you  want  recursion  and  want  to
       preserve  almost  everything  (with -H being a notable omission).  The only exception to the above
       equivalence is when --files-from is specified, in which case -r is not implied.

       Note that -a does not preserve hardlinks, because finding multiply-linked files is expensive.  You
       must separately specify -H.
source manpages: rsync