Re: [Bug-ddrescue] Verify recovered data

[Antonio Diaz Diaz]

Hello Zeniff.

Zeniff Martineau wrote:
> I have the same issue:
> * ddrescue consistently gets zero errors, yet produces a different
> image every time.
> * Have already made 6 images saved to 2 different HDDs with different
> filesystems.
> * Imaging an entire 8GB Kingston flash drive (1 image contains 3 partitions)
> * ddrescue version 1.17 on Arch Linux

I guess you are reading the data through an USB port. Maybe this is the 
problem. I had to reduce the frequency of my RAM from DDR400 to DDR333 
because it trashed all my flash drives connected to the USB port!


> I thought it might be a bad flash drive...but, there are no errors in
> any logs caused by the flash drive (as far as I can tell)...

Ddrescue can't know if the data are really good or if the hardware is 
lying about it. Does ddrescue produce different images when reading from 
other devices?


> 1. If this is a bad flash drive, why is it reading files correctly
> with no errors, but only the images are bad?

I don't know. Are you sure that the files are always copied correctly?


> 2. If this is a bug in ddrescue, what can I do to help it get resolved

Providing a reproducible testcase.


> 3. If there is no workaround for this, is my best bet to just use
> rsync to copy the files and forget about making an image?

I doubt it.


> 4. Is there some way to merge the images to create a more correct
> version, similar to the multiple bad CDs example from the docs? (can't
> really use the doc example, though, because no ddrescue logs contain
> errors)

Ddrescue can't merge the images if the hardware does not report the 
errors. I think the only kind of files that can be merged in such 
circumstances are lzip-compressed files (using lziprecover).


> P.S. Sorry to reply to an older message. It's my 1st mailing list post
> and this unreplied-to message by matt456 from 2013-03-03 matches my
> problem exactly and I can't find any other info after searching all
> day.

Sometimes a message does not obtain any response, specially if nobody 
has any useful answer.


Regards,
Antonio.