The problem I had with buring dvd's is that you need to wipe the dv first... if your using dvdrw....
First you will need to download dvd+rw tools and install, if you have not done already...
the commands I used are:
dvd+rw-format -Z /dev/dvdrecorder -force // this will format the dvdrw
growisofs -Z /dev/dvdrecorder /filenametobackup // backup a file
Hope this helps