Da futurebook:

This does underscore one the vexing problems librarians and archivists are struggling with in this age: the fragility and difficulty of digital as a way of preserving content. Data rot, or the gradual decay of data from the medium that hosts it, is a major issue. CDs, depending on the quality, can be viable as little as five years; flash and hard drives survive about five to 10 years. Even data storage on the cloud is on physical machines somewhere that are vulnerable to power outages, electrical surges, temperature changes, poor insulation and a number of other physical factors that can lead to the degradation of data.

Tom Tivnan