Google loses data as lightning strikes
Relevant amusing bit from the Amazon FAQ: "S3 is designed to provide 99.999999999% durability of objects over a given year. This durability level corresponds to an average annual expected loss of 0.000000001% of objects. For example, if you store 10,000 objects with Amazon S3, you can on average expect to incur a loss of a single object once every 10,000,000 years."<p>I think my favorite part of that is "on average", as if you will be making repeated ten-million-year trials of this effectively brand new technology.<p>The point is that once you get into several nines of reliability, really rare events that are impossible to model start to dominate your risk budget.