I think it is important that backups are kept in hard drives rather than optical media. optical media deteriorates fast and becomes unreliable after a bunch of years, I never thought them as usable backup storage mediums.
I used to have backups on CDs which I then transferred to DVDs (with some data loss) and now I have in hard drives because it's a lot more reliable. A hard drive put away, stored safely, will last more than a bunch of CDs, DVDs or BDs. The declining prices on storage also make this option economically possible nowadays. Anybody can have a home made NAS and pile up HDDs.