In article , says...
CD's and DVD's don't last forever. They sometimes don't last very long
at all. There is a fair bit of info on the web.

http://www.itl.nist.gov/div895/caref...dlingGuide.pdf
http://www.mscience.com/longev.html

There is also a serious consideration of how you will ensure there will
be equipment to read your storage media available and working. This
could easily be a problem in 20-50 years.

Just include plans to build the retrieval apparatus.

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A hard copy of the plans on archivally correct paper.