| 摘要 |
<p>Data integrity and availability is assured by preventing a node of a distributed, clustered system from accessing shared data in the case of a failure of the node or communication links with the node. The node is prevented from accessing the shared data in the presence of such a failure by ensuring that such a failure is detected in less time than a secondary node would allow user I/O activities to commence after reconfiguration. The prompt detection of failure is assured by periodically determining which configuration of the current cluster each node believes itself to be a member of. Each node maintains a sequence number which identifies the current configuration of the cluster. Periodically, each node exchanges its sequence number with all other nodes of the cluster. If a particular node detects that it believes itself to be a member of a preceding configuration to that to which another node belongs, the node determines that the cluster has been reconfigured since the node last performed a reconfiguration. Therefore, the node must no longer be a member of the cluster. The node then refrains from accessing shared data. In addition, if a node suspects a failure in the cluster, the node broadcasts a reconfigure message to all other nodes of the cluster through a public network. Since the messages are sent through a public network, failure of the private communications links between the nodes does not prevent receipt of the reconfigure messages.</p> |
