[Fwd: Power Down]

[Bob Canup]

Bob Canup wrote:

> Vipin Malik wrote:
>
> > Bob Canup wrote:
> > >
> >
> I can't see any difference between erasing a bad sector after the next power
> up and the case of a slightly earlier power failure where the data was never
> written in the first place; you wind up with an identical file system in both
> cases.  If you can survive the case of the earlier power failure failing to
> record the sector then you can survive the case of the bad sector being
> erased.
>
> The only difference that I see is that in the case of the bad sector  you
> know something happened, in the case of the data never being recorded you
> don't.
>
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On the way home last night it occurred to me that if you are doing a
read-modify-write cycle that it does make a difference where the error occurs.
In this case if the sector is never written the old data is still valid.

It seems to me the wear leveling necessary in a flash can be a benefit here; if
I understand correctly we don't overwrite the physical pages - only when a page
is 'committed' does the chip change its mapping so that it appears that the
sector was overwritten.





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