It is quite possible that Tux3 will get to incremental and online fsck before
Ext4 does. (There you go, Ted, that is a challenge.) There is no question that
this is something that every viable, modern filesystem must do, and no,
scrubbing does not cut the mustard. We need to be able to detect errors on the
filesystem, perhaps due to blocks going bad, or heaven forbid, bugs, then
report them to the user and *fix* them on command without taking the volume
offline. If that seems hard, it is. But it simply has to be done.