Re: [Bug-ddrescue] Feature request: copy bad sectors to sparse file

[Antonio Diaz Diaz]

Hi Ole,

Ole Tange wrote:
> I have said it before, but it cannot be repeated too often: Thanks you
> for ddrescue.

You are more than welcome.


> It would have been really handy if I could have copied the bad sectors
> onto a sparse file, then overlayed the device with the sparse file,
> mounted it, and copied the files off the disk:

This seems like a very ingenious hack. :-)

I think I have not understood how the overlay works. The data is read 
from the overlay file, and the holes in the overlay file are read from 
the device? If this is the case, you may need to run ddrescue a third 
time to fill the holes left in the overlay file by truly unreadable 
sectors (see below).


> I would imagine all you have to do is ignore the blocks that succeeds
> reading in the first try, and do as normal for all the rest.

I think you can achieve the effect of '--onlybadblocks' by running 
ddrescue twice and discarding the output of the first run:

  ddrescue -fNn /dev/baddevice /dev/null mylog
  ddrescue --sparse /dev/baddevice overlayfile mylog

and perhaps this:
  ddrescue -r1 --sparse /dev/zero overlayfile mylog


Hope this helps.
Antonio.