RE: Unstable bits and JFFS2

[Artem Bityutskiy <dedekind1@gmail.com>]

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On Fri, 2012-04-13 at 12:40 -0400, Atlant Schmidt wrote:
> Artem:
> 
> > Yeah, thanks for correcting. Yeah, read/write-disturb may make bits
> > to become unstable, but we assume this is a slow process which will
> > gradually make more and more bits flip and ECC will take care of
> > that. So I think Matej can exclude this.
> 
>   Unfortunately, ECC can only fix those PEBs that
>   are actually read. If one of the PEBs in your
>   filesystem is being used entirely to contain
>   obscure data that only gets read once in a
>   blue moon (i.e., very rarely), then multiple
>   read-/write-disturbs can hit accumulate in
>   that PEB and when it is finally read, it may
>   already contains too many errors to be
>   corrected by the ECC.
> 
>   We've seen this exact scenario occur with the
>   current UBI/UBIfs and will be implementing a
>   userland "scrubbing" system to ensure that
>   every PEB gets read at least once in a while
>   (e.g., weekly or whatever interval seems right).

This is right, people should have a user-space app which periodically
reads all /dev/ubiX_Y. Care to send a patch against mtd-www with some
explantion of this issue and extend the unstable bits issue?

But in Matej's case I do not believe he is testing long enough to hit
this scenario. But everything is possible of course.

-- 
Best Regards,
Artem Bityutskiy

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