The virtue of dependent failures in multi-site systems

A multi-site system consists of a collection of locallymanaged networks called sites, each containing a collection of processors. In this paper, we present the multi-site threshold model: a new failure model for multi-site systems that accounts for failures of sites. Using this model, we then derive quorum constructions that have two interesting features. First, they generate quorum systems that are more available than majority quorums. Second, our constructions reduce quorum sizes compared to the majority construction, thus reducing load on the processors and increasing the total capacity of the system. To show that our model is realistic, we discuss the implementability of this new model, motivating with data from a real system.