MMC quirks relating to performance/lifetime.

[Arnd Bergmann]

On Friday 11 February 2011, Lei Wen wrote:
> > Several orders of magnitude. It is very easy to get a card that can write
> > 12 MB/s into a case where it writes no more than 30 KB/s, doing only
> > things that happen frequently with ext3.
> >
> 
> Maybe we could get that case into mmc_test code, so that we could track
> that in latter whether it already be fixed or not? Or in other word, to prove
> the firmware in sd card is stupid or not. :)
 
There are many kinds of stupid, and a lot of cards are. I've actually had
excellent success with simply measuring from user space, which is
much easier than in mmc_test.

Unfortunately, you have to write to the card to do that, which may destroy
the data even if you write the same data that is already on it.

See
https://wiki.linaro.org/WorkingGroups/KernelConsolidation/Projects/FlashCardSurvey
for most of my results. I'm about to write up a better paper with all the
measurements, and will make my tools available soon.


	Arnd