Runtime filesystem consistency checking

There's a bigger problem: it is possible to tell a disk to write something somewhere, and it reports success, but has actually either written something different, lost it entirely, or overwritten something different. Local consistency checks on read would detect the first two cases, but no local check can spot the third case, as far as I can see. (This case is certainly not common, though: I have seen only one disk problem that was possibly attributable to this class of failure. I've been trying to get info on the frequency of this sort of missed-seek or mis-seek error, but all I can find is rumours. The secrecy of disk manufacturers regarding info critical to the integrity of one's data is quite distressing at times.)