[Yaffs] Re: bit error rates

[Peter Barada]

On Thu, 2006-02-16 at 12:43 +1300, Charles Manning wrote:
> On Thursday 16 February 2006 02:25, Jon Masters wrote:
> > On 2/10/06, Charles Manning <manningc2 at actrix.gen.nz> wrote:
> > > I think an interrupted erase is probably more likely to cause
> > > problems, but again this is just a hunch.
> >
> > I wonder how we could implement logic to detect this.
> >
> > > Dealing to an interrupted write is relatively straight forward. It
> > > will always be the last page written before the system went
> > > down. Most of the time (except for the last page written to a
> > > block), we can detect the last page because it is the  last page
> > > in the currently allocated block.
> >
> > I don't think this is currently testing on mount though.
> 
> That is correct, it is not being done at present. I was thinking as to how it 
> might be done.
> >
> > > It would be nice to improve this, but as Jon sayas, I think data
> > > integrity should always come first!
> >
> > Other people seem to disagree with my previous suggestions and I'm not
> > saying I can't be wrong in the matter :-) But I've not seen excessive
> > numbers of blocks being marked bad (except when fixing the OOB
> > code...) with read ECC failures. I accept though that this might just
> > be good old fashioned paranoia so if one of the vendor folks on this
> > list can comment, it would really help.
> 
> Some people have reported seeing a large number of blocks (~30-50%) being 
> retired on some devices. That's obviously not a GoodThing, but I'd like to 
> see what % of units failed. Then, how does one measure and evaluate this?
> 
> To my mind, if you ship 1000 units and half of them lose 30-50% of their 
> blocks in a year of normal use, that's probably a BadThing. If this only 
> happens on 1% of shipped units it might be an OKThing (depending on your 
> perspective).

Well my perspective would be BadThing if its either 1% or 50% of the
units suffering block losages like that.  In either case, you end up
with 30-50% of your available space being lost.  Imagine a 1GB iPod type
device that after a year turns into a .5Gb iPod.  I can imagine
customers would get pretty bent out of shape over that...

> However, losing data is also a BadThing.
> 
> It's one of those rock-and-hard-place sandwich choices. Any mods will be 
> configurable to allow current semantics.
> 
> -- Charles
>