Re: [Bug-ddrescue] Verify recovered data

[Scott Dwyer]

I have seen this same sort of issue with a particular USB to IDE/SATA 
adapter that I have. The IDE part works like it should, but the SATA 
part will not report errors and will return garbage data where the 
errors are (maybe it was data from the previous read, maybe not, point 
is not good data). What this means is that somewhere (in my case the USB 
adapter) something was not designed to properly handle errors. Perhaps 
that SATA CD/DVD drive just doesn't know how to properly handle the 
errors and report them. Also could be that the operating system (or 
computer) is not playing well with the drive (they are not working with 
the same protocol standards and don't know how to talk to each other 
properly). None of these things were designed with data recovery in 
mind, especially the cheap ones!

In any case, the important thing would be to figure out what is not 
working properly, and then don't use it again for future recovery attempts!

Scott

On 2/6/2014 2:22 PM, Antonio Diaz Diaz wrote:
> Reon Toerien wrote:
> > When working via USB ports results can be unreliable, nature of the 
> > beast.
>
> Not only USB ports. :-(
>
> I have been doing intensive testing with the next version of ddrescue 
> and have discovered a SATA CD/DVD drive with the same problem.
>
> I was trying to get a correct copy from two damaged CDs. I tried three 
> times with different settings, but the drive always returns wrong data 
> without signaling an error for at least one sector. The wrong data 
> returned coincides with the data of some nearby good sector, so I 
> guess the drive is returning the data from a previous read.
>
> I tried the same two CDs on another computer (with an older IDE 
> driver), and ddrescue got the correct image at the first try.
>
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