Re: [Bug-ddrescue] GNU ddrescue 1.23-pre1 released

[Scott Dwyer]

I would like to point out that shifting data could be very dangerous in 
certain conditions. First, depending on which direction you wish to 
shift the data, you would need to copy in the appropriate direction, or 
you could completely corrupt the data. Second, if there were any bad 
sectors at all, then there could be skipping with multiple passes along 
with trimming and scraping passes, which could cause much data 
corruption. And even if you have the correct direction and only one pass 
without skipping, a bad sector would cause the whole cluster to be bad, 
unless you choose a cluster size of 1 (very slow copy). Only if you used 
very specific and correct options could this be done in any sort of safe 
way.

Scott


On 3/17/2017 11:49 AM, Antonio Diaz Diaz wrote:
> Hello Gábor,
>
> Gábor STEFANIK wrote:
> > >     * The new option '--same-file' has been added. It allows infile 
> > > and outfile to
> > > be the same file or device. This can be used to test the writing 
> > > ability of a
> > > drive. It can also be used to copy part of a file to another 
> > > location inside or
> > > beyond the end of the same file if '--input-position' and 
> > > '--output-position'
> > > are different.
> >
> > Are overlaps handled correctly (like bitblt)? That is, can I safely
> > use this feature to e.g. shift a 20GB partition backwards on a disk
> > by 2GB?
>
> Interesting question. :-)
>
> Overlaps are not handled at all (and there are no plans to do it. 
> Shifting data is just a side effect of '--same-file', not the main 
> task of ddrescue). But you can possibly shift your partition safely if 
> you chose the right copy direction. I'll run some tests and will 
> document the findings in the description of '--same-file' in the manual.
>
>
> Thanks,
> Antonio.
>
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