On 05/29/2018 06:33 AM, Robert Heller wrote: > >> The UUID in the EFI boot options is 99E275E7-75A0-4B37-A2E6-C5385E600CB, which >> does not to match anything, but the system is only happy booting the old >> disk... > And at this point, it will only boot in legacy mode off the old disk. That's what I meant, I think. Legacy mode is BIOS-compatible. If you're booting in legacy mode, you can't access the UEFI variables. The old disk probably has GRUB installed on the first block. It might be booting in legacy mode *because* the UEFI boot option's UUID doesn't match your partition. You might want to disable legacy mode entirely. Boot a rescue disk if needed, and fix the boot option from there.