[siebenmann]

Unfortunately ZFS scrubs are not as complete as fsck on a regular filesystem. ZFS scrubs only verify that checksums are intact. They don't verify that filesystem level metadata is correct (although they do verify ZFS structural metadata as part of walking everything, which isn't the same thing). For example, a ZFS scrub will not detect that a filesystem inode has certain sorts of crazy or invalid contents, or damaged ACLs. It doesn't even necessarily verify that the filesystem directory structure is correct and intact.

For more on this, see https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSScrubLim...

(The tl;dr is that a fsck on an ordinary filesystem has to walk the directory tree to find everything. However, ZFS maintains a separate list of active inodes and a scrub can just walk over them and check the checksums of all of their data blocks. It doesn't have to, for example, read a directory's contents to find further files to scrub.)