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

Claudio Lanconelli
2007-11-26T14:00:26Z

Ricard Wanderlof wrote:
> On Fri, 23 Nov 2007, David Brown wrote:
>
>
>> Flash should be reasonably immune to degradation from reads. In fact,
>> it is fairly resiliant to degradation at all.
>>
>
> I beg to differ; we ran some tests here on a 256 Mbit NAND flash where I
> work which showed a marked degradation in read integrity if the block had
> been written many times. For this particular chip in the setup used, after
> 100 000 read/write cycles, non-correctable ECC errors started popping up
> after about 43 million reads. For blocks that had only been written a
> couple of times, we didn't detect any read errors whatsoever after 4.5e+10
> reads (during three months of continuous reading of the same block).
>
> I would however love to see some hard data, or at least an application
> note, on the frequency of various errors. Most of the information I've
> seen is of the 'it is a known fact that ...' - type, without any
> references. And the data sheets seem very silent on this subject, only
> acknowledging the fact that bit flips do occur.
>
Hi,
I find very useful this paper, it talks about "read disturb" on page 22:
http://www.edn.com/contents/images/ToshibaNANDFlash1.pdf

Cheers,
Claudio Lanconelli