Re: Problems when writing DVDs with growisofs

[scdbackup@gmx.net]

Hi,

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> Short before end an I/O-Error happens and was logged to the kernel log
> file as:
>  attempt to access beyond end of device
>  hdd: rw=0, want=8388608, limit=8388604
>  Buffer I/O error on device hdd, logical block 2097151
> Then I umounted the device and uses dd to copy an image of the dvd to 
> my harddisk:
> I mounted the image via loop-device and tried again to cat all files
> to /dev/null which again fails as described above.

Up to this point i would say the DVD did not accept all
data that were sent to it. (Swallowed a last buffer full)

But...

> Then I used readcd to create an image of the dvd. Also this process
> does not report any error.
> I mounted the image via loop device and THIS time I was able to
> retrieve all files. They were identical to the originals.

Now the DVD-ROM driver of the operating system is under
suspicion. (We had and still have this effect with CDs.)

Compare the size of the images extracted by dd and readcd.
How much larger is the one of readcd ?


> I am near desparation. I cannot find the reason for this
> behaviour. Since I copy more valuable data as some dvb-t recordings to
> DVD I would be happy to have a reliable scheme how to copy
> successfully files to DVD+RW and other media.

The ill effects with CD readers are traditionally compensated
by generous padding. 300 kB are considered to be enough.

You may try to add a designated victim file to the ISO
image but better would be to split the jobs of mkisofs
and growisofs and to add the padding *after* the ISO image.
  mkisofs ... >buffer_file
  dd bs=1m count=10 if=/dev/zero >>buffer_file
  growisofs ... -Z /dev/hdd=buffer_file
or
  mkisofs ... >buffer_file | \
  let_through_and_pad_10_mb | \
  growisofs ... -Z /dev/hdd=/dev/fd/0

let_through_and_pad_10_mb would add 10 MB of zeros after
it first passed all stdin unaltered to stdout.
(I use the latter method in my backup tool.
Out of mere superstition i still pad 300 kB to DVDs.)


Have a nice day :)

Thomas