Abstract
Quorum is a graceful concept on solving the mutual exclusion problem in distributed systems. It could provide high fault-tolerant ability and low communication cost in distributed processing. A quorum O is a subset of elements in the system that a process has to collect the permissions of every member in O before it is allowed to execute a mutually exclusive action. A valuable quorum structure should have small quorum size and high availability. In this thesis, we study on the availability analysis of some typical quorum structures. We find a way to either promote the availability or minify the quorum size throgh a tree-based quorum design strategy. In particular, we present a variation of the crumbling walls, which keeps O(√N)quorum size, but its availability is improved to possess the asymptotic property, N is the number of nodes in the distributed system.