Yeah, it's double-layered or something like that. Holds a BUNCH more information, but loading times can be sluggish - though I doubt that would be a problem with Prime Trilogy, particularly if you squeeze the games onto individual layers. Remember that Prime and Echoes were on Gamecube-sized discs. So put those two on one and Corruption on the other.
(Is it clear I have virtually NO idea what I'm talking about?)
I know what the double-discs are, but Brawl already caused quite a lot of disc read errors, imagine what this would do...