UBI/UBIFS: dealing with MLC's paired pages

[Boris Brezillon]

On Fri, 25 Sep 2015 08:30:23 +0000
Karl Zhang 张双锣 (karlzhang) <karlzhang at micron.com> wrote:

> 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.

Don't be sorry, and there's no wrong opinion: the whole point of this
discussion is sharing our ideas and arguing to find the best solution.

Regarding the use of extra OOB bytes, I'll follow Richard's opinion:
let's keep it as a 'last resort' solution if we fail to find an
acceptable alternative.

Best Regards,

Boris

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