[Yaffs] Re: power fail testing

[Sergei Sharonov]

Charles,

> 2) If an ECC failure is detected on a block, then the block=20
> is retired.=20
> Perhaps instead a block should only be retired if a write=20
> fails. This would=20
> be more in tune with Toshiba's recommendations. The argument=20
> against this has=20
> been that I'd rather retire blocks earlier (ie before they=20
> start to go bad),=20
> but this should be reviewed in the light of recent evidence.

I see block leakage during power cycling test. I think it is=20
caused by read failures on partially programmed pages. Blocks
should not go bad after few hundred erases. On a positive side
the leakage is moderate - a dozen lost blocks after ~500 cycles.

Now, I got a question about erasing during power fail. AFAIK this
is what was killing original jffs - incompletely erased blocks had
bits that after programming sometimes read 0 and sometimes 1, e.g.
write verify may be successful but a later read may fail. That was
the reason for introduction of the "clean marker" in jffs2.
YAFFS does not use clean markers at the moment. The problem
is harder to catch because of much faster erase of the NAND, but
it is probably still there. Thomas, is that correct recollection of=20
the jffs/jffs2 and clean marker situation?

Sergei
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