it's not the CD, it's not the drive, it's not both - it's their relationship

[gusl]

DVD1(Ubuntu) works with ExternalDrive
DVD2 works with DesktopDrive
DVD2 does not work with ExternalDrive

It seems I've found a new domain for relational learning!
It doesn't seem very hard to think of other bipartite relational domains in chemistry and engineering (e.g. the friction between pairs of surfaces).

Anyway, I'm using DesktopDrive to create an ISO of DVD2 and writing to my External HD... then I will use external HD to burn a DVD; Finally I will try the copy on ExternalDrive.