I have Ubuntu 20.10 on zfs root (upgraded from 20.04) I tried to restore 20.04 using zsys features at boot, which was unsuccessful. I have a backup (created using syncoid). Using zfs send/receive. I created a new pool in a separated disk called spool. It has a restored 20.04 before the upgrade.
I'd like to be able to choose at boot time between the two rpools. How to I set it up with grub.