https://unix.stackexchange.com/questions/252936/grub2-boot-to-a-second-another-hard-disk
/boot/grub2
cat device.map
(hd0) /dev/sda
(hd1) /dev/sda
/boot/grub2
cat device.map
(hd0) /dev/sda
(hd1) /dev/sda