Re: SD-card endurance, wear and crappiness

[Arnd Bergmann <arnd@arndb.de>]

On Tuesday 09 September 2014 10:54:51 Johan Rudholm wrote:
> 2014-09-03 16:24 GMT+02:00 Johan Rudholm <jrudholm@gmail.com>:
> > Hi all,
> >
> > as you know, NAND flash can be programmed a limited number of times
> > before it reaches end of life, the number of times varies with the
> > NAND technology used, among other things.
> >
> > As far as I can tell from the simplified SD-spec, there is no way of
> > asking the card about how many program/erase cycles it can handle, or
> > how many p/e cycles are left before reaching EOL. Right?

I think that is correct.

> > So, if one should want to give the user some kind of early warning
> > that it's time to change SD-cards, is there a way? Also, when a card
> > has reached EOL, is there a way of telling this condition apart from
> > all other error conditions that may arise? As you know, depending on
> > the quality of the card and controller, read timeouts, write timeouts,
> > lockups etc may occur but can usually be fixed with a power cycle.
> >
> > I'm thinking of collecting simple statistics from for instance
> > card/block.c and exposing it via an ioctl or sysfs. The statistics can
> > be gathered and processed by some user space process which can
> > determine if the user needs to be alerted. The statistics can be, for
> > instance:
> >
> > * Writes/reads that timeout, but succeed after a retry
> > * Writes/reads that timeout and never succeeds
> > * Different kinds of errors in the card status
> > * Anything else?
> >
> > Perhaps it's not possible to detect worn out cards this way, but at
> > least it could point out and warn about crappy cards?
> >
> > Any thoughts about this?

Have you tried if this works? In my experience, the worn-out cards
I have either just fail completely, or they return incorrect data,
but I have not looked at this side of the problem much.

Do you have cards that sometimes time out but always still return
correct data on retry?

	Arnd