Testing DVD writing drive

[kleiman-jjUpw6JcT4r2fBVCVOL8/A at public.gmane.org (Steven L. Kleiman)]

 I got my new computer, and the first thing I tried to do was to make a
set of recovery disks.  It keeps failing; it writes the first disk and
then tries to verify it and says it doesn't verify.  I've made 3
coasters this way.
 -SLK-09Jun15> Perhaps the disks are ok, but the verification fails
because of a DMA problem.  Such is the case with my two Dell Laptops.
This problem is mentioned in the Ubuntu documentation at
 https://help.ubuntu.com/8.04/installation-guide/powerpc/boot-troubleshooting.html
which suggest checking if DMA is currently enabled, and if so, then
explains how to disable it.
 -- Steve