The Most Long Lastingest Storage?

What digital storage can retain information the longest? Recordable CD/DVDs only last a couple of years. A decade at most. Barring catastrophic disk failures, HDs seem to last the longest, but what about Flash Memory? These types of memories are increasing in capacity rapidly and they don't have any moving parts.

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Well, you might.  Could be family pictures for example, but that's  I suppose rather trival.  A Geomorpholoigist I know wants to revisit the data from his doctoral dissertation.  The school still has it of course--on the old IBM .75in magnetic tape and printouts.  Box upon box of faded printouts.  Guess which one he's forced to use?

To repeat:  This is a serious problem.  How to store immense amounts of data long term AND be able to access it.
Ideas anyone?