The distinction between
/usr has historical reasons. Back when Unix
systems were booted from two tapes, a small root tape and a big user tape.
Today, we like to use different partitions for these two spaces. The Hurd
throws this historical garbage away. We think that we have found a more
flexible solution called union filesystems, which allow to create virtual
filesystems which are the union of several other filesystems. However, support
for union filesystems is still in early development.