Some questions on bit-flips and JFFS2

[Ricard Wanderlof]

On Mon, 3 May 2010, Thorsten Mühlfelder wrote:

> PS: I could not reproduce the bit-flip problem. It just happens in rare cases.
> Furthermore some of my devices are using Samsung NAND instead of the Micron
> NAND and did not show any problems yet. So perhaps my problem are just some
> bad NAND chip? But still I have to find a solution for the problem.

In our experience, which is limited to 32 MiB and 128 MiB SLC flashes, 
Micron, Hynix and Numonyx have much worse bit read error rates that 
Samsung and Toshiba, even though the data sheets hint at the same level of 
data integrity. We made some random tests, reading again and again from 
the same flash partition, and the first group above tended to show 
uncorrectable ECC errors already after less than a million reads, whereas 
the second group showed only single-bit errors even after 20 or even 60 
million reads.

Of course, reading that many times from a flash partition, especially a 
boot partition, is hardly realistic, but in our experience, it simulates 
quite well the situation of a having a seldom-read boot partition in a 
flash where there is activity going on in other parts of the flash, i.e. 
an embedded system where a single flash chip provides all non-volatile 
storage, over a long period of time.

Of course these are random samples only, but they've been very consistent 
so far. Lately a new batch of Numonyx 128 MiB flashes arrived which seem 
to have better error rates. One can speculate as to why but I'll leave 
that discussion off this mailing list.

/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