[OT] legality of DVD backup

[Richmond]

My EFL school is slowly migrating from a mixed Mac and Ubuntu school to 
being
a 100% Ubuntu school. However, for some reason which escapes me DVD playback
on my Ubuntu boxes is, at best, "lumpy".

Therefore I am proposing to make ISO images of all the DVDs that I own 
and use on
a regular basis onto the hard disk of my main content delivery machine; 
I will always
have the physical DVDs present in the classroom.

This will allow my Ubuntu box to play my DVDs normally.

Can anyone advise me as to the legality of this action?

Morally I have no qualms whatever; without this process I would have to,
either, purchase a TV and a DVD player, or, a Mac.

sincerely, Richmond.