UBI/UBIFS: dealing with MLC's paired pages

[Karl Zhang 张双锣 (karlzhang)]

Hi Boris

Something else suggestions. 

We know that using the OOB area to store UBI metadata(Backup data) is not a good idea, this is just a thinking, and also do a little work to implement it and verification .

For paired page issue from MLC is troublesome, we are trying our best to deal with it. Although attempt to use some bad ideas.

> > Only NAND provides an OOB area. 
Some devices(NOR) do not have OOB, simultaneously, they do not have paired page issue, right?  I think they do not need to store a redundant metadata to anywhere.
AFAIK , only MLC(TLC maybe) NAND need store some metadata for another copy, and try to protected it by ECC.

But, if OOB have some unused area (at least 48 bytes) and the chip has paired page issue , could we take a little advantage of them  to reduce UBI fail rate? 

Above, is just some thinking , wish we can have some better solutions. 
As Bean said, most customer do not want UBIFS crash, and so do we.

Thanks to your patient to point out my wrong opinion.


BR



-----Original Message-----
From: linux-mtd [mailto:linux-mtd-bounces at lists.infradead.org] On Behalf Of Boris Brezillon
Sent: Friday, September 25, 2015 3:30 PM
To: Bean Huo 霍斌斌 (beanhuo)
Cc: Iwo Mergler; computersforpeace at gmail.com; dedekind1 at gmail.com; richard at nod.at; shuangshuo at gmail.com; rnd4 at dave-tech.it; Jeff Lauruhn (jlauruhn); linux-mtd at lists.infradead.org; Stefan Roese; dwmw2 at infradead.org
Subject: Re: UBI/UBIFS: dealing with MLC's paired pages

Hi,

On Fri, 25 Sep 2015 00:43:37 +0000
Bean Huo 霍斌斌 (beanhuo) <beanhuo at micron.com> wrote:

> > And 3:
> > Only NAND provides an OOB area. Other flash devices like parallel or 
> > SPI NOR don't. And we definitely want to continue supporting 
> > platforms with such flash devices and UBI (and UBIFS).
> > 
> > Thanks,
> > Stefan
> > 
> For MLC NAND paired pages issue, we have developed two methods to 
> solve it in UBI layer, We hope that every expert on UBI/UBIFS can give more suggestions about how to improve and perfect it.
> I think ,this week, I can submit first solution patch out. Currently do coding style.

Are you referring to the suggestion proposed by Karl (using the OOB area to store UBI metadata), or is this something else?

Best Regards,

Boris

--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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