Comment by goku12

Sounds a lot like the A/B update method used widely in Android and to a lesser extend for embedded GNU/Linux OTA updates. But it uses two distinct boot partitions. Since ZFS is involved here, I assume that boot environments take advantage of its copy-on-write mechanism to avoid duplicating the entire boot dataset.

NixOS and Guix use a concept called 'system generations' to do the same without the support of the filesystem. LibOSTree can do the same and is called 'atomic rollback'.

Talking about NixOS, does anybody know of a similar concept in the BSD world (preferably FreeBSD)?