Problem with NAND memory data retention

Problem with NAND memory data retention

[Lukasz Majewski]

Dear All,

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.


[1] -
http://www.sst-ic.com/File/Seriea/PDF/100923163334f47b2ce6-13b7-43d0-9b8c-ec1c75ca2c6f.pdf


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@denx.de

Re: Problem with NAND memory data retention

[Ricard Wanderlof]

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.

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.

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
-- 
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
Phone +46 46 272 2016                           Fax +46 46 13 61 30

Re: Problem with NAND memory data retention

[Lukasz Majewski]

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.

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@denx.de

Re: Problem with NAND memory data retention

[Andrea Adami]

On Thu, Apr 27, 2017 at 3:04 PM, Lukasz Majewski <lukma@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

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@denx.de
>
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/

Re: 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@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@denx.de
> >
> > ______________________________________________________
> > Linux MTD discussion mailing list
> > http://lists.infradead.org/mailman/listinfo/linux-mtd/
> >




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@denx.de