Re: [gentoo-embedded] embedded ext2 and fsck

[Ed W]

On 06/04/2010 22:20, Marcus Priesch wrote:
> however after some months of operation the device failed to boot with
> exact the same error message ...
>
> the reason i suspect was that due to power failures the ext2 got
> inconsistent somehow ... which resulted in "stale NFS file handle
> messages" ... not very intuitive ;)
>


It would be interesting to hear if these errors "go away" by switching 
to EXT3?

There seem to be several things happening here:

1) The CF card is quietly shuffling data around, so in theory it might 
move a good sector onto a patch of flash which is worn out, causing it 
to be corrupted on next read.  Similarly when you "write" the card does 
quite a lot of work in the background and theoretically if power was 
lost during the shuffling around of sectors this could also cause data loss?

2) Sudden shutdowns causing the ext2 to be marked dirty and causing 
subsequent problems (ie not fully read-only mounted

To be honest, I don't know a lot about how ext2 is mounted read-only, 
but option 2) above seems unlikely...?

This suggests that there are real problems with CF cards getting old and 
the wear levelling causing data to be shuffled onto worn out sectors.  
And/Or it may prove that the wear leveling causes corruption if power is 
removed during a write and sectors are only partly shuffled (which kind 
of makes sense).  Both ideas don't seem to be well talked about and 
there is huge disagreement about the probable lifetimes of various flash 
devices?  Certainly I haven't ever had a bad device so I have never 
really seen how they fail?  However, I have experienced wierd 
corruptions (on windows!) with certain devices if I unplug them suddenly 
(ie they loose power suddenly) while they are writing - this could 
indicate that certain devices have poor implementations of wear levelling?

Interesting stuff... However, if switching to ext3 fixes things then 
this sounds like an OS issue and not a CF card issue?

Cheers

Ed W