The road to data longevity consists of:
- Redundancy (multiple copies of your data)
- Verifiability (checksums of the data files, stored with the copies and separately)
- Properly safe and stable storage (no light, no significant temperature changes, little or no air pollution)
- Regular and repeated verification (create new checksums and check against your old ones)
- Regular and repeated migration (copy your data to new media well within the life expectancy of the old media)
NASA learned much of this the hard way.
And, as others have suggested in other forums, take particular care with the data you care about. That could be e.g. photographs that are keepers, exhibit or portfolio grade, "memories" and family pictures. In these instances, back up RAW data as well as processed data.
Don't worry too much about the longevity of the CD or DVD media. Yes, there have been concerns, particularly with pre-printed media and rewritable media, but CD-R, DVD-R and DVD+R have - in most cases - many years of life expectancy, probamost likely greater than that of magnetic media, as long as they're stored properly. High speed tape backups sound real nice, but are also quite expensive for a single person, family or small business.
But you will have to migrate your data to new media once every few years anyway, as you upgrade your computer or hard disks. Take those opportunities to re-verify everything.
Now professionals like Jonathan or Michael with terabytes of data probably don't like the idea of verifying the integrity of their accumulated data all at once, so I expect it makes more sense to do this more frequently and of subsets of the data, perhaps "continuous" verification makes sense.
It's time consuming and expensive to take care of your data, as opposed to just putting it on a hard disk and forget about it. There are no fast roads, no cheap tricks. But even though it isn't fast or cheap, it's faster and cheaper than it was ten or twenty years ago.
