Problem with NAND memory data retention

[Lukasz Majewski]

Hi Andrea,

Thanks for your response!

> On Thu, Apr 27, 2017 at 3:04 PM, Lukasz Majewski <lukma at denx.de>
> wrote:
> 
> > Hi Ricard,
> >
> > >
> > > On Thu, 27 Apr 2017, Lukasz Majewski wrote:
> > >
> > > > I'd like to ask you for sharing your experience with NAND Flash
> > > > devices
> > > > - which may be older that their data retention time.
> > > >
> > > > I've a problem with Flash NAND memory (Samsung 128Mx8).
> > > >
> > > > In the data sheet [1] the manufacturer claims that it has 10
> > > > years for data retention. The device equipped with it is a bit
> > > > older than 10 years.
> > > >
> > > >
> > > > How one can diagnose that data retention time for NAND Flash has
> > > > been exceeded?
> > > >
> > > > Is that:
> > > >
> > > > - The number of bit flip errors on a RW page so large that ECC
> > > > cannot fix it?
> > > >
> > > > - Or are whole RW pages erased (0xFF)/corrupted/cleared (0x00)?
> > > >
> > > > - Or any other evidence?
> > > >
> > > > Thanks in advance for your help.
> > >
> > > I think the interpretation is that the manufacturer guarantees
> > > that under the circumstances specified (temperature, supply
> > > voltage, erase cycles etc) that the data will be retained for at
> > > least ten years, beyond that it's just not specified. It doesn't
> > > mean that something catastrophic will happen after ten years,
> > > i.e. ten years is not a hard limit beyond which things start
> > > going haywire.
> >
> > Thanks for your explanation.
> >
> > >
> > > I can't say I have experience with old NAND flashes loosing their
> > > data, but technically I would expect that what happens is that
> > > eventually the charge leaks away from the bit cells, causing bit
> > > flips, quite simply, so it's the same mechanism that requires the
> > > flash to be 'scrubbed' periodically to check if the data needs to
> > > be rewritten.
> > >
> > > I.e. it's the first case in your list, the number of bit flips
> > > increases.
> >
> > Unfortunately with my device I do experience the second scenario.
> >
> > I do observe pages read as zeros.
> >
> 
> Hello,
> 
> I think I have seen the same issue: one defective device did not
> respond to CFI QRY.
> 
> http://lists.infradead.org/pipermail/linux-mtd/2014-May/053872.html

I do not have (yet) the CFI commands dump, but in my case Erase->
Reflash sequence causes the file content to be correct.

IMHO, If the Flash memory controller itself is broken, then
"re-flashing" would not help.

Maybe - in my case the NAND flash driver (2.6 kernel) causes the issue
(with zero filled page showing up in the middle of a YAFFS file) by some
write done at mistakingly calculated address?

Any ideas/hints are more than welcome :-)

Best regards,
Łukasz Majewski

> 
> These devices were sold in 2002-2003 so they are now >15yrs old and I
> have two of them working flawlessy.
> 
> Regards
> Andrea
> 
> 
> 
> 
> >
> > For example in the middle of a file - page sized (2K) data is read
> > as zero. And this file is RO (no modification). And such zero read
> > is persistent - happens all the time. The only way is to replace
> > the whole file (erase it and write again).
> >
> > We use yaffs file system.
> >
> > And such errors pop up in random places.
> >
> > >
> > > The fewer erase cycles that a given flash block has seen, the less
> > > wear there has been on the insulation, and the better the
> > > retention would be. The ten year spec is under the worst case
> > > condition of the maximum number of erase cycles having been
> > > performed on the flash.
> > >
> > > /Ricard
> >
> >
> >
> >
> > Best regards,
> >
> > Lukasz Majewski
> >
> > --
> >
> > DENX Software Engineering GmbH,      Managing Director: Wolfgang
> > Denk HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell,
> > Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email:
> > wd at denx.de
> >
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> >




Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de