The Zombie Stack Exchanges That Just Won't Die
Tools exist for adding redundancy in archiving, for example DVDisaster, which fills your DVD's leftover space with recovery information, allowing more physical degradation than usual of the disk.
Is this strategy worth the bother when archiving? One obvious alternative is to refresh your backup media more often, and use redundancy of actual physical copies, rather than redundancy per-disk.
Another downside is the possibility that DVDisaster software becomes unmaintained and unusable.
Supposing this per-medium redundancy strategy isn't a waste of time, what alternatives exist to DVDisaster?
occulus
The best alternative I'm aware of are the parity archive parchive formats, which let you do the same thing but in a media independent fashion and using open source tools.
However, your time might be better spent simply burning a second DVD or putting a copy on another medium. Data disks like CDROMs and DVDs already use low-level error detection and correction codes, making bit loss relatively unlikely (I suspect) compared to whole disk failure (cracks, breaks, scratches, ink failure, etc.)
I second the usage of Parchive (or other tools with similar functionality), but want to emphasize that in the end you should get a system where you have a set of disks (like a RAID) where you can tolerate a loss of any one disk and rebuild it from the remaining ones.
This is better than having ability to recover a scratch from any disk, but failing to tolerate the complete disk loss, because they will fail over time one way or another, and you need a solid replacement strategy anyway.