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  1. In mission critical distributed systems, unavailability is typically not an option. Typical resilience goals might be three nines after the dot, six nines in extremely crucial settings, and so on. So the really interesting part is the top right corner, where individual component failures may give you only one or two nines guarantee, i.e., p=.9 or p=.99; in this zone, quorums boost the resilience significantly.

    Note that, most of the area in the graph intuitively follows from simply observing that the expected number of failures (1-p)*n is more than the resilience bound.

    A very old starting point where quorum systems have been evaluated is: Y. Amir and A. Wool. Evaluating quorum systems over the Internet. In Proc. 26’th IEEE Symp. Fault-Tolerant Computing (FTCS), pages 26–35, Sendai, Japan, 1996.

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