Some news for this: [PATCH] [MTD] BLOCK_RO: Readonly Block Device Layer Over MTD ?

[Ricard Wanderlof]

On Wed, 21 Nov 2007, Jörn Engel wrote:

> > Won't ECC take care of spurious bit flips?

> Single-bit, yes.  Once you accumulated a bunch of them in proximity, it
> may no longer work.

Yes that is true of course.

Does anyone know of any tests or evaluations run on NAND flash chips, more 
than what can be found out from the data sheets?

We ran some tests on an ST 256 Mbit flash here to try and get some grip on 
the various bit flipping mechanisms.

At least for this chip, it seemed that if a block has only been written a 
few times, then there seems to be virtually no limit to how many times it 
can be read without bit flips occurring (the test ran for three months 
with continuous reading of the same block, during which over 4.5e+10 
reads were performed). On the other hand, if the block was written the 
maximum specified number of times (100 000 for this chip), bit flips would 
start occurring after 15 million reads.

(We also wrote a block far over the specified limit, about 1.7 million 
times. In this case, bit flips during read started occurring after about 
200 000 reads.)

Of course, this was a random sample of a single chip type used in a 
specific hardware environment, so it would be interesting to see if anyone 
else has done any similar test.

/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