Comment 2 for bug 1721317

Without rebooting I followed directions at https://askubuntu.com/questions/83037/how-do-i-reinstall-grub2, mounted / and /boot/efi:

root@ubuntu:~# df
Filesystem 1K-blocks Used Available Use% Mounted on
udev 16421252 0 16421252 0% /dev
tmpfs 3287460 9792 3277668 1% /run
/dev/sdc 1550400 1550400 0 100% /cdrom
/dev/loop0 1496320 1496320 0 100% /rofs
aufs 16437292 2260244 14177048 14% /
tmpfs 16437292 18012 16419280 1% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 16437292 0 16437292 0% /sys/fs/cgroup
tmpfs 16437292 524 16436768 1% /tmp
tmpfs 3287460 84 3287376 1% /run/user/999
/dev/sdb2 50264772 53072 47635316 1% /mnt
/dev/md0 523248 3496 519752 1% /mnt/boot/efi
root@ubuntu:~# ls /mnt/boot/efi
EFI
root@ubuntu:~# ls /mnt/boot/efi/EFI/
Dell ubuntu
root@ubuntu:~# grub-install --root-directory=/mnt /dev/sdb
Installing for i386-pc platform.
grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won't be possible.
grub-install: warning: Embedding is not possible. GRUB can only be installed in this setup by using blocklists. However, blocklists are UNRELIABLE and their use is discouraged..
grub-install: error: will not proceed with blocklists.
root@ubuntu:~# grub-install --force --root-directory=/mnt /dev/sdb
Installing for i386-pc platform.
grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won't be possible.
grub-install: warning: Embedding is not possible. GRUB can only be installed in this setup by using blocklists. However, blocklists are UNRELIABLE and their use is discouraged..
Installation finished. No error reported.
root@ubuntu:~# update-grub
/usr/sbin/grub-probe: error: failed to get canonical path of `aufs'.
root@ubuntu:~#

Tried to boot from BIOS (UEFI boot manager) selecting "integrated RAID Controller 1: ubuntu" and got a "GRUB>" prompt. Seems like no way to boot from second drive via the UEFI BIOS. Swapped drives with same result.

or similar hoping