The Load and Availability of Byzantine Quorum Systems

TL;DR

This paper introduces four new constructions for Byzantine quorum systems that optimize load and availability in a hybrid fault model, extending previous work to tolerate both benign and Byzantine failures.

Contribution

The paper presents four novel $b$-masking quorum system constructions with optimal load or availability in a hybrid fault model, and proves lower bounds for these metrics.

Findings

Four $b$-masking quorum system constructions with optimal load or availability.

Lower bounds established for load and availability in the hybrid fault model.

Extensions to tolerate both benign and Byzantine failures.

Abstract

Replicated services accessed via {\em quorums} enable each access to be performed at only a subset (quorum) of the servers, and achieve consistency across accesses by requiring any two quorums to intersect. Recently, $b$-masking quorum systems, whose intersections contain at least $2b+1$ servers, have been proposed to construct replicated services tolerant of $b$ arbitrary (Byzantine) server failures. In this paper we consider a hybrid fault model allowing benign failures in addition to the Byzantine ones. We present four novel constructions for $b$-masking quorum systems in this model, each of which has optimal {\em load} (the probability of access of the busiest server) or optimal availability (probability of some quorum surviving failures). To show optimality we also prove lower bounds on the load and availability of any $b$-masking quorum system in this model.