Re: [PATCH v3 0/6] NAND BBM + BBT updates

[Ivan Djelic <ivan.djelic@parrot.com>]

On Tue, Jan 17, 2012 at 11:19:19AM +0000, Angus CLARK wrote:
> On 01/13/2012 10:36 PM, Artem Bityutskiy wrote:
> > On Thu, 2012-01-12 at 10:09 +0100, Sebastian Andrzej Siewior wrote:
> >>
> >> so the OOB array is by design more reliable than the data area?
> > 
> > I think so, because it is distributed, and it is historically the way
> > blocks had been marked as bad, and I thing vendors make sure this
> > mechanism works.
> > 
> 
> Is this really true?  I was under the impression that the OOB area was the same
> as the data area, as far as reliability is concerned, and is subject to the same
> ECC requirements.
> 
> As far as I am aware, NAND manufacturers only guarantee that the
> factory-programmed OOB BB markers are valid.  Nothing is mentioned in the
> datasheets about using OOB BB markers to track worn blocks - they all tend to
> recommend BBTs.
> 

Hello,
FWIW, my experience with NAND manufacturers totally confirms what you are saying;
i.e. OOB is no different technology, and factory bad block markers are not
always even implemented in OOB: hardwired tables -- probably efuses -- are
sometimes used to systematically return 0x00 bytes when a bad block is read;
which has the advantage of preventing SW from accidentally erasing a factory
bad block.
BR,

Ivan