[KennyBlanken]

You don't need to fix anything.

ZFS automatically self-heals an inconsistent array (for example if one mirrored drive does not agree with the other, or if a parity drive disagrees with the data stripe.)

ZFS does not suffer data loss if you "suffer a total disk failure."

I have no idea where you're getting any of this from.

[lazide]

If the data on disk (with no redundant copies) is bad, you’ve (usually) lost data with ZFS. It isn’t ZFS’s fault, it’s the nature of the game.

The poster built a (non redundant) zfs pool on top of a hardware raid6 device. The underlying hardware device had some failed drives, and when rebuilt, some of the underlying data was lost.

ZFS helped by detecting it instead of letting the bad data though like would normally have happened.

[fulafel]

The parity cannot be used in the degraded scenario that was under discussion.

See eg here where the increasing disk size vs specified unrecoverable read error rate is explored in relation to the question at hand: https://queue.acm.org/detail.cfm?id=1670144 (in the article Adam Leventhal from Sun, the makers of ZFS, talks about the need for triple parity).

Also, the conclusion "ensure your backups are really working" is an important point irrespective of this question, since you'll also risk losing data due to buggy software, human errors, ransomware, etc.