Re: data loss on jffs2 filesystem on dataflash

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > I glanced at the manual. Uhh, DataFlash is very specific beast. It 
> > suppoers page program with built-in erase command... So DataFlash 
> > effectively may be considered as a block device. Then you may use any FS 
> > on it providing you have wrote proper driver? Why do you need JFFS2 then 
> > :-) ?
> 
> Still can't.  Block devices have the attribute that writing AAA... to
> a block containing BBB... gives you one of three possible results in
> case of power failure:
> 
> 1. BBB...BBB all written
> 2. AAA...AAA nothing written
> 3. AAA...BBB partially written.
> 
> Flash doesn't have 3, but two more cases:
> 4. FFF...FFF erased, nothing written
> 5. AAA...FFF erased, partially written
> 
> Plus the really obnoxious
> 6. FFF...FFF partially erased.  Looks fine but some bits may flip
>    randomly, writes may not stick, etc.
> 
> Now try finding a filesystem that is robust if 4-6 happens. ;)

ext2 and anything that does not do journalling?

I do not thing behaviour on powerfail is part of block device definition.

				Pavel
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