RE: Unstable bits and JFFS2

Artem Bityutskiy
2012-04-13T16:58:47Z

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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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