Differentiated Availability in Cloud Computing SLAs

Cloud computing is the new trend in service delivery, and promises large cost savings and agility for the customers. However, some challenges still remain to be solved before widespread use can be seen. This is especially relevant for enterprises, which currently lack the necessary assurance for moving their critical data and applications to the cloud. The cloud SLAs are simply not good enough. This paper focuses on the availability attribute of a cloud SLA, and develops a complete model for cloud data centers, including the network. Different techniques for increasing the availability in a virtualized system are investigated, quantifying the resulting availability. The results show that depending on the failure rates, different deployment scenarios and fault-tolerance techniques can be used for achieving availability differentiation. However, large differences can be seen from using different priority levels for restarting of virtual machines.