content: I think a (cheap) solution would be to keep up moving data from storage media to storage media from time to time. One thing technology has that books do not is digest hashes. With them one can guarantee too copies are, in fact, copies. So let's say I have this DVD I burned 8 years ago and that I can still read from. I move this data to a BD today (conveniently with data from other DVDs because BDs can store more data) and I keep doing so every ~10 years. If this is done correctly, the data can be preserved (theoretically) forever.