A figure-of-merit, BLERmax, provides a reasonable approximation to the customer's perception of the integrity of data stored on KODAK Writable CD and Photo CD Media. When determining data life, using the industry standard specification of BLERmax less than or equal to 220 requires extrapolation far beyond the range of the data. Consequently, we have used the criteria BLERmax less than or equal to 50. The change of the figure-of-merit has been found to follow an Arrhenius model. That model predicts (at the 95% confidence level) that 95% of properly recorded discs stored at the recommended dark storage condition (25°C, 40% RH) will have a lifetime of greater than 217 years.
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TDK rates the archival lifespan of its cyanine-based CD-R discs at 70 years (based on accelerated aging tests). This paper presents data that reflect TDK's decade-long research and development efforts in the field of optical recording media.
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For years now many media manufacturers have performed their own lifetime evaluations using these or a variety of other homegrown tests and mathematical modeling techniques. Historically, manufacturers have claimed life-spans ranging from 50 to 200 years for CD-R discs and 20 to 100 years for CD-RW.
Soure (very good article overall).
The bottom line is that, depending on who you believe media can last a long time. Generally speaking, if you treat it like crap, it will deteriorate much faster. If you treat it well, it will last quite a while. The above quotes relate to CD-Rs, as my example number of 100 years was for CD-R. My Google search for "DVD-R longevity" was not as informative as the "CD-R longevity" search was. I suspect DVD-R longevity will be roughly comparable to CD-R longevity.
I try to use quality media and store them on a bookshelf that is out of direct sunlight, away from my radiator and in a relatively cool office. I am not worried about my media going bad. But then, I still keep serveral archived copies of anything important, should something go bad, chances are not all copies will go bad.
\Dan