CD/DVD Verify

[Paul Howarth]

Jonathan Allen wrote:
> Paul Howarth wrote:
>> You could read back the data from the CD device using dd and then 
>> compare what you get back with the original ISO.
> 
> Thank you for the suggestion.  I just tried:
> 
>    # dd if=/dev/cdrom of=file

Try:
# dd if=dev/cdrom of=file bs=2048

> and got a clutch of errors like:
> 
>    hdc: command error: status=0x51 { DriveReady SeekComplete Error }
>    hdc: command error: error=0x50 { LastFailedSense=0x05 }
>    ide: failed opcode was: unknown
>    end_request: I/O error, dec hdc, sector 1904, 1912, 1920, etc in turn
> 
> What does that mean ?  The result produces a file 901120 bytes long, when
> the original ISO file is 987136 bytes long, but at least at the front they
> look pretty identical to 'od -c'
> 
> When the drive is mounted, all the files on the CD seem OK and don't
> generate any media errors.

Given that the length of the resulting file is *less* than that of the 
original ISO, I suspect that there is a problem with the recording. If 
you got a resulting file that was *bigger* than the original ISO then 
that might not be an issue, as you could have read back some of the 
lead-out data after the end of the filesystem; as long as the files are 
identical up to the length of the original ISO, all should be OK but 
that's not the case here.

Paul.