Should 'cpio' backup only unmounted filesystems?
Should a 'cpio' backup file be restored to a mounted device?
Can 'cpio' interact with /dev/root, /dev/u, /dev/stand directly?
cpio is not smart, it just opens directories and files, stat's inodes, reads or writes. Unmounted will either automount or not be available, as configured. It reads files when creating archives and can create dirs as well as files on unpack.