How to rip movie dvd with copy protection?

I'm trying to rip a movie dvd to an ISO image. When I try to copy it, at the beginning it seems like everything is working fine. But when it reaches around 650MB (I guess that's the start of the main movie which is copy protected), it becomes unbelievably slow or the program isn't reacting anymore. I've tried it with dd, ddrescue, mkisofs and K3b. I'm using a LG GP08NU6W as an external dvd drive and I'm running Arch Linux.