Since running separate /usr without mounting it from initramfs on top of / before init is and has been broken with udev for a long time now[1][2][3]
[1] http://bugs.gentoo.org/show_bug.cgi?id=364235 [2] http://fedoraproject.org/wiki/Features/UsrMove#Move_all_to_.2Fusr [3] http://www.freedesktop.org/wiki/Software/systemd/separate-usr-is-broken Can we warn users about not doing the separate /usr mistake in the handbook?
