zfs mirroring rpool/bpool

[Harry Putnam]

I read that the zpool incantation for mirroring the way zfs is
configured for rpool and bpool when one uses the installer zfs option
would be something like:

  zpool attach bpool /dev/sda1 /dev/sdb1
  zpool attach rpool /dev/sda2 /dev/sdb2

As noted at:
https://askubuntu.com/questions/1238363/using-ubuntu-20-04-with-zfs-new-install-how-can-i-add-a-second-drive-to-create

That appears to be somewhat off the mark

And in fact when I looked with fdisk it appears its sda3 to sdb3
                                                    sda4    sdb4

fdisk /dev/sda . . .

Device       Start       End   Sectors  Size Type
/dev/sda1     2048   1050623   1048576  512M EFI System
/dev/sda2  1050624   5244927   4194304    2G Linux swap
/dev/sda3  5244928   9439231   4194304    2G Solaris boot
/dev/sda4  9439232 167772126 158332895 75.5G Solaris root

Of course, one of the aims is to end up with either disk bootable.

So what about the efi (sda1) and swap (sda2)

At any rate I Guess what ever partitions are required would need to be
exactly matched to the existing sda partitions.

A few clues as to how to arrive at that would be handy here.