A loooong time age (OpenSolaris days) I had a system that had corrupted its zfs. No fsck was available because the developers claimed (maybe still do) that it's unnecessary.

I had to poke around the raw device (with dd and such) to restore the primary superblock with one of the copies (that zfs keeps in different locations on the device). So clearly the zfs devs thought about the possibility of a corrupt superblock, but didn't feel the need to provide a tool to compare the superblocks and restore one from the other copies. That was the point when I stopped trusting zfs.

Such arrogance…