A Methodology to Evaluate the Trustworthiness of Cloud Service Providers' Availability

Cloud service providers (CSPs) compete among each other to guarantee very high availability of their services. The most common CSPs guarantee the availability of at least 99.9% (some even 100%) in their service level agreements (SLAs), i.e., they guarantee maximum 8.77 hours of downtime per year for their services. However, this high guarantee does not imply that they comply with their SLAs. Many reports addressed that CSPs' downtime is much greater and usually the cloud consumer's costs cannot be covered by CSP's indemnification. On the other hand, the service availability is not a decisive factor for many cloud consumers. That is, many cloud consumers are interested in lower cost for an acceptable level of availability. In this paper, we define a new methodology to evaluate the CSPs according to the cloud consumers' needs. We introduce a very important factor, i.e., trustworthiness beside the availability. With our methodology, the cloud consumers can quantify the trustworthiness and the security of their potential CSPs, in order to migrate their services to the most appropriate CSP. Our evaluation shows that Google is the best choice of the evaluated CSPs in trustworthiness, although it offers the worst availability in its SLA, compared to other most common CSPs.