I don't get it. Why do people back up on DVDs? It's slower, not a reliable. Why not just use a external HDD and backup with time machine? Doesn't everybody do that? Hearing people talking about backing up with discs sounds sooo 2002.
I've had many hard drives fail. I've never had an optical disc fail. I make archival backups to 25 gb Blu-ray discs. I have a Time Machine volume for my hourly backups and I do a once a month backup with a hard drive I keep at separate buildings than where my Macs are. So, I have 3 copies of everything on hard drives and one copy on optical media.