This one works pretty much as the directions describe. I suggest copying the linux image (vmlinuz...) and the ram disk image (initramfs...) and /boot/efi/EFI/redhat/grub.cfg so that if something goes wrong, there's a way back. The dracut command they suggest remakes the initramfs and the other part of the procedure redoes /boot/efi/EFI/redhat/grub.cfg. The main trick was to put boot=UUID=xxxxxxxx for the /boot partition; I was using /boot/efi/EFI/redhat since this was a UEFI system. It would probably make sense to make sure that there are /boot and /boot/efi partitions on both drives (a and b). That way if one disk craps out then the other could be made bootable. Right now /boot/efi is on A and /boot is on B.