[nwf]

A slight disagreement: the advantage of a ZFS online consistency checker would be to help ensure that there are no bugs in ZFS.

It appears that ZFS lacks a full consistency checker -- scrub only walks the tree and computes checksums; notably absent in this procedure appears to be validating the DDT. While ZFS claims to be always on-disk consistent--and I certainly believe that the intent is that it be so!--I seem to have tripped over some bug ( http://lists.freebsd.org/pipermail/freebsd-fs/2013-March/016... ) which corrupted the DDT, and now I have no way of rebuilding it, so I dropped $$$ (for me) on a new disk array and zfs send | zfs recv so that everything rebuilt. That's sort of crazy, if I may be so bold.

I suppose I could take the pool offline for several days and poke at it with zdb, but that is not really desirable either.