One thing I DO know (don't remember whether Tim King mentioned it to me, or
I read it somewhere) is that when a disk is validated there is a bit
somewhere in the root record that says "I think disk is ok". When a disk
is 1st written on, this bit gets reset (will cause disk-validator to
attempt recovery if it "sees" such a disk). The last thing that happens
after the 3 second delay, is the root is changed back to say disk valid.