Хай,
Вы можете делать только символические ссылки на каталоги.
Из man 7 symlink:
Hard links may not refer to directories (to pre‐
vent the possibility of loops within the file system tree, which would
confuse many programs) and may not refer to files on different file
systems (because i-node numbers are not unique across file systems).
Для создания резервных копий используйте rsync, dd или cpio (иногда вместе с tar, bzip2, gzip или zip).