This narrows the set to: DVD-R, DVD-RW, DVD+R, DVD+RW.
(DVD-RAM and DVD+R DL have significantly different sizes.)
You should try a different brand of media. Best a different
type. E.g. try DVD+R if the failing ones are DVD-R.
If all reachable kinds of DVD fail, then consider to exchange
the drive.
This narrows the set to: DVD-R, DVD-RW, DVD+R, DVD+RW.
(DVD-RAM and DVD+R DL have significantly different sizes.)
You should try a different brand of media. Best a different
type. E.g. try DVD+R if the failing ones are DVD-R.
If all reachable kinds of DVD fail, then consider to exchange
the drive.