> 
>> c) at least at first usage verify should be done after backup
>> dd if=/dev/rcd0a bs=1m of=/dev/null progress=1
>
> I'd suggest doing a real verify:
>
> 	dd if=/dev/rcd0a bs=1m of=some_tmp_file
> 	cmp original.iso some_tmp_file
> 	rm some_tmp_file
>
> I had one disk that had 16 bytes miscompare (out
> of an almost full 4.7 GB DVD)  IIRC it didn't have
> any read errors, so just dd-ing it to /dev/null
> wouldn't have caught the problem.

ins't your DVD drive broken? at least in theory correction code on DVD 
discs should at least always detect an error.