Re: [Bug-ddrescue] Reference to dvdisaster in manual

[Robert Mittendorf]

Minor amendment: dvdisaster can read RAW form CDS, but only from CDs.
For DVDs drives do not allow a RAW data access. Maybe in order to
prevent 1:1 copies of protected disks (afaik Error Correction Code of
CDs is placed in the subchannels that were often used by copy protection
techniques)

So I think that is the only condition under which dvdisaster can help
without pre-calculated external disk-redundancy: A CD that is accesses
RAW instead of logical.

On 12/07/2017 12:54 PM, Gadgetmind wrote:
> On 2017-11-20 15:29, address@hidden wrote:
>> dvdisaster can only recover discs that generated ECC data for and not
>> generic disks with read errors?!
>
> That is also my reading.
>
> A few years ago, I created a tool that used what's called a
> "CatWeasel" card in a PC to read raw MFM sectors off some damaged
> floppies, recover what it could of data (ignoring if required damaged
> sector headers), and then create an output file of what it had got
> along with "goodness" flags. I could then do multiple runs with
> different drivers and settings and merge the results of a few passes.
>
> This didn't get all the data so I wrote a new tool that used the
> quality of the MFM interleaved clock bits to suggest which areas where
> bad and I could then use bad raw sectors from multiple runs, and if
> required brute force, to try and get a good CRC32.
>
> I ended up getting every scrap of data off 15+ floppies that had been
> in my loft for 30 years but it did take three months of part-time coding!
>
> A tool *could* use similar techniques for DVDs and perhaps merge good
> data after C2 from multiple runs to try and get good data to feed into
> C3 but dvdisaster doesn't seem to do this, so the good results story
> seems to be more good luck.
>
>