But the catch is that undestanding "why" it happens is most likely the
key to solution... Why or why recording just hung half-way and most
mysteriously failed with "INVALID ADDRESS FOR WRITE" after a long
while... Is there a chance that the drive was opened by another program
during failed recording?
No, I am quite sure that did not happen. The only user programs running
during the backup were an editor and latex. I can't think of any daemons
that would access /dev/dvd. I don't think that updatedb ran and even
then I don't think that it would open /dev/dvd. *But*...
I occasionally mount a dvd to check it contents, and then forget to
umount it before rewriting it. I cannot be certain that I didn't do that
on this occasion.
growisofs does unmount media prior recording. If it fails to, it won't
start the recording. So you can keep forgetting to unmount it:-), but
you shouldn't "stand" in it (I mean if you cd /mnt/dvd, then attempt to
unmount /mnt/dvd fails with "resource busy," and recording won't start).