Is your rpool mirrored? On a test enviroment if I detach one of the drives, I can run update- grub. Reattaching the drive breaks update-grub.
I'm currently stuck in 19.04 because of this bug. # zpool status pool: zroot state: ONLINE scan: scrub repaired 0B in 2h59m with 0 errors on Sun Oct 13 03:23:12 2019 config: NAME STATE READ WRITE CKSUM zroot ONLINE 0 0 0 mirror-0 ONLINE 0 0 0 sda3 ONLINE 0 0 0 sdb3 ONLINE 0 0 0 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1848856 Title: Upgrade from 19.04 to 19.10 with zfs on root fails with grub syntax error To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1848856/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs