Ubuntu Desktop 20.04 supports a single ZFS boot drive out of the box. I wanted a ZFS mirror, without going through an entirely manual setup of Ubuntu as described by OpenZFS in their instructions for Ubuntu 20.04 and instructions for Ubuntu 22.04
This adds a mirror to an existing Ubuntu ZFS boot drive after the fact. It's been tested on Ubuntu 20.04 by me and all the way up to Ubuntu 22.10 by users in comments.
ZFS requires native encryption to be added at pool / dataset creation. Ubuntu 22.04 supports this during installation. Whether these instructions are suitable for mirroring such a setup has not been tested. For Ubuntu 20.04, these instructions are not suitable for creating an encrypted ZFS boot disk, please use the full instructions linked above for that. You can, however, add an en