The availability of cloud-based services: Is it living up to its promise?

Cloud-based services have spread among customers, boasting a number of advantages over centralized and self-owned infrastructures. Clouds providers claim a higher resilience, due to the use of a large distributed array of servers and storage facilities. However, assessments of their actual availability are missing. Here an early attempt to provide a third-party assessment is presented. Though not disposing of first-hand measurements, we have collected data on outages from a number of sources. We use those data to evaluate the frequency and duration of outages. The average duration of outages appears to lie in the 8-10 hours range, with a significant dispersion. A statistical analysis through QQ-plots and mean excess plots shows that the tail of the distribution of outage durations is well modelled by a Generalized Pareto distribution.