Recent changes to udev mean that it is now a requirement to have the partition containing the /usr filesystem mounted prior to system boot, requiring usr and root to be on the same partition (which is Red Hat’s preferred solution), or to mount /usr prior to booting from an initrd.
I’ve successfully run Linux systems for many years without needing this additional complication, and I don’t plan to start changing the core boot process in order to comply with Red Hat’s (non-FHS compatible) vision of what a Linux system should look like.
The best alternative right now seems to be Busybox‘ mdev – a very simple hotplug agent and /dev tree maintenance tool which provides identical core functionality to udev.
However, the default configuration files provided with mdev are somewhat outdated and there isn’t much information out there documenting how to make the transition.