It depends on what type of DVDs you want to back up. For copy protected DVDs they have programs like "Any DVD Cloner Platinum" which will clone any DVD regardless of copy protection taking anywhere from 90 minutes to 4 hours, depending on the quality you want. If you want a perfect clone (with all special features and menus) you're going to have to buy double density blank DVDs which can be a bit expensive. Or you can just use the cheaper 4.7 GB blanks. Most people can't tell any quality difference.