[DVDnav-discuss] Invalid IFO for title XX (VTS_XX_0.IFO)

[Loïc Minier]

On Mon, Nov 22, 2010, Loïc Minier wrote:
> On Mon, Nov 22, 2010, John Stebbins wrote:
> > dd exits when it encounters an error.  So you have an incomplete ISO.
> > You need to use something like ddrescue with such discs.
> 
>  Yep; as I noted, I'm using conv=noerror with dd so that it keeps going,
>  writing zeroes in place of the bytes it couldn't read.  I believe
>  dd-rescue does the same thing, albeit with retries, but retries
>  wouldn't help anyway.

 Well, I was completely wrong in my expectations of dd; if any block
 fails, it just gives up on the whole block.  dd_rescue is different in
 that it has two configurable block sizes: one as long as everything
 goes well, and another one to retry failing reads.  I was passing
 bs=100M or something stupidly large to dd, which means that any read
 error (due to copy-protection mechanisms) caused a 100M hole in the
 .iso file.  With dd_rescue, I'm passing something large as the regular
 block size and 4096 for the block size of failed reads (found with
 blockdev --getbsz on the dvd drive).

 I could copy and play this failing DVD using dd_rescue.

 Sorry for rejecting your proposal, I was wrong!

-- 
Loïc Minier