NAND BBT corruption on MPC83xx

[Atlant Schmidt]

Mike:

> It is not a permanent damage thing.

  A "read disturb" does no permanent damage to the chip
  but if the read disturb event involves more bits than
  can be corrected by your ECC code, it can do permanent
  damage to the *DATA* you've stored in that block.

  For this reason, a good flash management system manages
  to at least occasionally read through *ALL* of the in-use
  blocks in the device so that single-bit errors can be
  scrubbed out (read and successfully corrected) before
  an adjacent bit in the block also fails (which would
  eventually lead to a multi-bit error that might be
  beyond the ability to be corrected by the ECC).

  As far as I know (and I'm sure the list will correct
  me if I'm wrong! ;-) ), neither UBI nor UBIFS nor any
  Linux layer provides this routine scrubbing; you have
  to code it up yourself, probably by accessing the
  device at the UBI (underlying block device/LEB) layer.

                        Atlant

-----Original Message-----
From: linux-mtd-bounces at lists.infradead.org [mailto:linux-mtd-bounces at lists.infradead.org] On Behalf Of Mike Hench
Sent: Saturday, June 18, 2011 13:55
To: Scott Wood; Matthew L. Creech
Cc: linuxppc-dev at lists.ozlabs.org; linux-mtd at lists.infradead.org
Subject: RE: NAND BBT corruption on MPC83xx

Scott Wood wrote:
> As for the corruption, could it be degradation from repeated reads of
that
> one page?

Read Disturb. I Did not know SLC did that.
It just takes 10x as long as MLC, on the order of a million reads.
Supposedly erasing the block fixes it.
It is not a permanent damage thing.
I was seeing ~9 hours before failure with heavy writes.
~4GByte/hour = 2M pages, total ~18 million reads before errors in that
last block showed up.

Cool. Now we know.
Thanks.

Mike Hench



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