Fault tolerance
Machine failures, Communication faults, storage device crashes, and decays of storage media should be tolerated by the system to some extent. A fault tolerant system must continue to function may be with degraded form when these failures are encountered. The degradation is able to be either in performance or functionality or both. The majority commercial systems provide only limited fault tolerance. Though, fault tolerant systems are difficult to implement and in the DEC VAX cluster, multiple computers are permitted to share a set of disks. If a system breaks down, users are able to still their information from another system. Though, if a disk fails after that all the systems will lose access.