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: [email protected]
[mailto:[email protected]] On Behalf Of Mike Hench
Sent: Saturday, June 18, 2011 13:55
To: Scott Wood; Matthew L. Creech
Cc: [email protected]; [email protected]
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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