weird dvd burning issue

[Rashkae]

Reply *way* below :)

andy baxter wrote:
> hello,
> 
> I have just encountered a weird issue when trying to burn an iso image 
> of a data dvd. I used k3b to do the burn, at 2x speed to an external usb 
> dvd burner. In k3b, the verification phase of the burn failed. Also, 
> when I md5sum /dev/scd0 it returns a different sum from md5summing the 
> iso image.
> 
> However, when I did:
> 
> root at monkey:~# diff -qr /mnt /media/cdrom0 | tee iso.diff
> 
> there was no output and iso.diff was empty, so there is no difference in 
> the files on the dvd. I then tried copying /dev/scd0 back to the hard 
> disk using:
> 
> root at monkey:~# dd if=/dev/scd0 of=/home/andy/Desktop/64studio-from-disk.iso
> 1633856+0 records in
> 1633856+0 records out
> 836534272 bytes (837 MB) copied, 107.058 s, 7.8 MB/s
> 
> When I list the two files together, the one copied back from the dvd is 
> slightly longer than the original iso:
> 
> root at monkey:~# ls -l /home/andy/Desktop/64*
> -rw-r--r-- 1 andy andy 836503552 2008-08-13 02:40 
> /home/andy/Desktop/64studio_2.1_i386.iso
> -rw-r--r-- 1 root root 836534272 2008-08-13 07:38 
> /home/andy/Desktop/64studio-from-disk.iso
> 
> ('64studio-from-disk.iso' is the one copied back by me; the other is the 
> original).
> 
> Does anyone know what is going on here, and whether this is a known 
> issue? My dvd drive reports itself as a 'freecom optical disk drive' in 
> lsusb.
> 

I'm afraid I don't know why k3b verification is failing..

With regards to the other issues, this is normal.  dd will always read
past the end of the image and grab some null bytes on DVD's.

You need to use isoinfo program to determine the correct size of the iso
for dd to copy.

Example:

isoinfo -d -i /dev/scd0

The output will include:

Logical block size is: 2048
Volume size is: 2089612


Then you plug those into dd (the 2048 should be a constant, I think)

dd if=/dev/scd0 bs=2048 count=2089612 of=sample.iso (or pipe it into md5sum