  State-of-the-art asynchronous Byzantine fault-tolerant (BFT) protocols, such
as HoneyBadgerBFT, BEAT, and Dumbo, have shown a performance comparable to
partially synchronous BFT protocols. This paper studies two practical
directions in asynchronous BFT. First, while all these asynchronous BFT
protocols assume optimal resilience with 3f+1 replicas (where f is an upper
bound on the number of Byzantine replicas), it is interesting to ask whether
more efficient protocols are possible if relaxing the resilience level. Second,
these recent BFT protocols evaluate their performance under failure-free
scenarios. It is unclear if these protocols indeed perform well during failures
and attacks.
  This work first studies asynchronous BFT with suboptimal resilience using
5f+1 and 7f+1 replicas. We present MiB, a novel and efficient asynchronous BFT
framework using new distributed system constructions as building blocks. MiB
consists of two main BFT instances and five other variants. As another
contribution, we systematically design experiments for asynchronous BFT
protocols with failures and evaluate their performance in various failure
scenarios. We report interesting findings, showing asynchronous BFT indeed
performs consistently well during various failure scenarios. In particular, via
a five-continent deployment on Amazon EC2 using 140 replicas, we show the MiB
instances have lower latency and much higher throughput than their asynchronous
BFT counterparts.
