If you find yourself in a position in which you're running Arch Linux and your file systems are based on LVM, RAID, or both, and when you upgrade your kernel your system won't boot because the kernel isn't running the lvm2 hook, here's how to fix it.
mount -t procfs proc /mnt/proc
mount -t sysfs sys /mnt/sys
mount -t tmpdevfs dev /mnt/dev
chroot /mnt
pacman -Syu
and watch your kernel being built.exit
and reboot
. remove your stick and boot into your now working arch linux.