Storage Will Be
Much Less Free
Than It Used To Be by David Rosenthal. post 
Cost data up to 2010. Industry consolidation, and the technical difficulties of migrating from PMR to HAMR, meant that already in 2010 the Kryder rate had slowed significantly and was not expected to return to its trend in the near future.
For the purpose of building a model of long-term storage economics, the endowment approach is essential; it effectively computes the net present value of the expenditures that data incurs through its history and allows apples to apples comparisons between different technologies.
Slowing of the Kryder rate should not have been a surprise. Here is Randall Munroe's explanation. xkcd . In the real world exponential growth can't go on forever, it is always just the steep part of an S-curve.