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."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.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.