Re: [Bug-ddrescue] Contents of the "bad" sectors in an image file

[Antonio Diaz Diaz]

Hello Bob,

Bob Bib wrote:
> I've made an image of a faulty drive with the help from dderescue.
> The status of the resulting mapfile is "finished", but still there
> are few dozens of bad sectors remaining. The resulting image
> "outfile" is an ordinary file on an ext4 FS.
>
> Can I expect that all the "bad" blocks in the image file contain only
> zeroes, or should I perform a "fill" pass just to make sure?

If outfile is an ordinary file created by ddrescue, then you may expect 
the bad blocks to contain zeros. If it were a device or a previously 
existing file, the bad blocks would contain the data previously present 
there.


> Unfortunately, in documentation, I haven't found an explicit
> indication of the outfile contents in the case of bad blocks.

The chapter 'Generate mode' of the manual[1] gives a hint, but I'll 
document this in the next version of ddrescue. Thanks.

[1] 
http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html#Generate-mode

"Ddrescue can in some cases generate an approximate mapfile, from infile 
and the (partial) copy in outfile, that is almost as good as an exact 
mapfile. It makes this by simply assuming that sectors containing all 
zeros were not rescued.

However, if the destination of the copy was a drive or a partition, (or 
an existing regular file and truncation was not requested), most 
probably you will need to restart ddrescue from the very beginning. 
(This time with a mapfile, of course). The reason is that old data may 
be present in the drive that have not been overwritten yet, and may be 
thus non-tried but non-zero."


Best regards,
Antonio.
--
http://www.thenational.scot/politics/16993191.jordi-cuixart-i-am-a-political-prisoner-held-hostage-by-spain/