Storage Technology Replacement Policy

There's an anomaly in this graph from my prototype economic model of long-term storage. It shows the endowment as a multiple of the initial storage purchase cost that would have a 98% probability of not running out of money in 100 years, plotted against the Kryder rate, the annual percentage drop in storage purchase cost.

The region between Kryder rates of 25% and 35% is flat. It seems strange that, with storage prices dropping faster, the endowment needed isn't dropping too. I finally got time to figure out what is going on, and I now believe this is an artefact of the technology replacement policy model I implemented as part of the prototype model. It isn't that the policy model is unrealistic, although there is plenty of room for disagreement about alternative policies. Rather, the parameters I gave the policy model to generate this graph were unrealistic. Follow me below the fold for what Paul Krugman would call a wonkish explanation.

Talk at PDA2012

I spoke at this year's Personal Digital Archiving conference at the Internet Archive, following on from my panel appearance there a year ago. Below the fold is an edited text of the talk with links to the sources.