My system is Gentoo Linux based booting off an LVM based root partition.
The system successfully boots through the initrd. It starts the init of the main kernel, but then fails when trying to check the root drive (/etc/init.d/checkroot).
The error reported is that the root drive (/dev/vg/lv) is unavailable for fsck.whichever.
[Note: I have figured out one solution to this problem, and am posting this to help others. If you know a better approach I'd love to hear about it!]