which already exist and have the same checksum and size on the
receiver are skipped. This option can be quite slow.
-dit(bf(-a, --archive)) This is equivalent to -rlptgoD. It is a quick way
-of saying you want recursion and want to preserve everything.
+dit(bf(-a, --archive)) This is equivalent to -rlptgoD. It is a quick
+way of saying you want recursion and want to preserve almost
+everything.
+
+Note however that bf(-a) bf(does not preserve hardlinks), because
+finding multiply-linked files is expensive. You must separately
+specify bf(-H).
dit(bf(-r, --recursive)) This tells rsync to copy directories
recursively. If you don't specify this then rsync won't copy