weird dvd burning issue

[andy baxter]

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.
>
> andy
>
>   
P.S. I have just successfully installed from the iso, so the difference 
is obviously not in the iso's boot sector.

andy