UBIFS recovery fails

[Atlant Schmidt]

All:

> On modern SLCs (at least I first saw it on 34 nm SLC flash), those bitflips
> can be _unstable_, i.e. they can appear and disappear randomly as you read
> pages. I experienced this phenomenon only on pages which were being programmed
> or erased during a power cut.

  This makes perfectly good sense. During erasing or programming,
  charge is being deposited-upon or removed from the floating gates
  and that's not an instantaneous process, so it can be interrupted
  while on-going, leaving a gate that's only half charged or half
  discharged.

  At that point, the floating gate may have charge on it that's
  all-too-near the threshold voltage for the cell and any given
  read of that cell could "go either way" depending on minute
  variations in other conditions.

                                   Atlant

-----Original Message-----
From: linux-mtd-bounces at lists.infradead.org [mailto:linux-mtd-bounces at lists.infradead.org] On Behalf Of Ivan Djelic
Sent: Wednesday, October 19, 2011 06:23
To: Ricard Wanderlof
Cc: linux-mtd at lists.infradead.org; Jean-Sébastien Gagnon
Subject: Re: UBIFS recovery fails

On Wed, Oct 19, 2011 at 07:50:42AM +0100, Ricard Wanderlof wrote:
> That said, it seems to me that power failure during write causing
> excessive bitflips would be a problem with any flash, not just MLC or
> modern "unstable" SLC. Ivan, you said you've only seen it with modern
> flashes, not older SLC ?

Excessive bitflips after a power failure happen on all types of flash (SLC,
MLC, even NOR flash); it is an expected possible consequence of the power cut.
It is not really a problem as long as what you read in flash is _stable_.

On modern SLCs (at least I first saw it on 34 nm SLC flash), those bitflips
can be _unstable_, i.e. they can appear and disappear randomly as you read
pages. I experienced this phenomenon only on pages which were being programmed
or erased during a power cut.

BR,
--
Ivan

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