I think the difficulty in these conversations is that people say they want a "fsck for ZFS", when often they don't mean they want "periodic sanity checks for ZF

I think the difficulty in these conversations is that people say they want a "fsck for ZFS", when often they don't mean they want "periodic sanity checks for ZFS", they mean they want something like "xfs_repair -d* for ZFS" or "extundelete for ZFS" - that is, a tool for salvaging beyond-the-pale mangling such that your pool is no longer able to be imported. * - not a perfect analogy, but I'm hard-pressed to think of good off the shelf tools for what they're looking for. I guess reiserfsck's infamously side-effect laden --rebuild-tree would probably be closest... (I am acquainted with zdb -r and import -T; neither helps you if there's not enough metadata consistent to get enough of a pool structure in memory to 'import', but one could still conceivably salvage some data in that case.)