Re: CD Life Expectancy
I had reason to look into this not long ago from the perspective of archiving laboratory test results for clinical trials which have to be kept for at least 10 years (FDA regulations).
All the reputable manfrs. put the shelf life of an unused CD-R WORM (Write Once Read Many) in the region of 5 years plus, and the readable life of a CD-R (once created) in terms of decades.
The client was pretty comfortable with 2 CD-Rs created and stored in different locations in addition to the magnetic tape archive (DAT, IIRC) plus the on-line disk storage being able to guarantee data availability for a minimum of 15 years.
Carefully stored (not exposed to extremes of heat / cold, direct sunlight, moisture, physical damage) I am confident that data written to a branded CD-R will remain readable for at least 20 years - many manfrs suggest 50 years plus based on accelerated testing results.
A commercially pressed Alu CD-ROM is expected to last over a century, subject to storage provisos above (oxidation of the Alu layer is the killer, but gold is a tad expensive!) - however, that doesn't help if you can't write to it!
Now CD-RW is a different kettle of fish entirely and I believe that the lifespan is much less, though I haven't investigated it.
DVD disks are different again, due to the much higher data density and shorter wavelength of laser used. I would expect these to be significantly shorter-lived than equivalent CDs.
My advice is to archive data that you want to keep for your lifetime only onto CD-R media (branded) rather than DVD. It may only store 1/6 of the data of a DVD, but it will probably keep it 6-times longer, and don't use re-writable media for long-term storage.
SD