Followup to DVD Burning question

[Søren Schmidt]

Arne Wörner wrote:
> --- Søren Schmidt <sos at DeepCore.dk> wrote:
> 
>>Arne Wörner wrote:
>>
>>>That's how I do backups with a DVD-RW:
>>>  tar cf - ... | dd of=/dev/acd0 obs=32k conv=osync
>>>
>>>Unluckily my DVD-RW's cannot be used for UFS with my
>>>burner... I do not know why.
>>
>>DVD-RW doesn't quite cut it for UFS, you need DVD+RW media for
>>that.
>>
> 
> Why? I can read and write the same block of a DVD-RW round robin.
> I mean:
> 
>>dd if=a of=/dev/acd0 bs=32k count=1 oseek=10
>>dd if=/dev/acd0 of= /dev/null bs=32k count=1 iseek=10
>>dd if=b of=/dev/acd0 bs=32k count=1 oseek=10
>>dd if=/dev/acd0 of= /dev/null bs=32k count=1 iseek=10
>>dd if=c of=/dev/acd0 bs=32k count=1 oseek=10
>>dd if=/dev/acd0 of= /dev/null bs=32k count=1 iseek=10
> 
> ...
> This looks just like a hard disc to me...

I forgot the exact details, but the DVD-RW media (or rather the DVD-RW 
method of accessing RW media) doesn't allow for non 32K transfers, 
whereas the DVD+RW method does read-modify-write behind the scene to get 
it to work seamlessly. I guess this could be worked around in the burner 
firmware but that would probably offend the DVD consortium ;)

-- 

-Søren