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Date: Mon, 26 Nov 2007 14:58:38 +0100
From: Claudio Lanconelli <lanconelli.claudio@eptar.com>
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To: Ricard Wanderlof <ricard.wanderlof@axis.com>
Subject: Re: Some news for this: [PATCH] [MTD] BLOCK_RO: Readonly Block Device
	Layer Over MTD ?
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Cc: David Brown <mtd@davidb.org>, Linux mtd <linux-mtd@lists.infradead.org>
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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