HP Integrity rx5670 Windows Integrity Cluster Installation and Configuration G - Page 17

NOTE Chapter 1 Introduction Cluster terminology MNS quorums have very strict requirements to ensure they work correctly, and therefore should only be considered by administrators who fully understand the issues involved in using MNS-based clusters. Their use should be limited to the following situations: • Geographically dispersed clusters-Involves a single MSCS cluster that has members in multiple geographic sites. While geographic clusters are possible using a standard quorum, a number of issues arise in terms of presenting the quorum as a single, logical shared drive among all sites. Majority Node Set quorums solve these issues by allowing the quorum to be stored on the local hard disk. HP does, however, support geographically dispersed clusters with shared quorums through the use of Cluster Extension XP (CLX) and Continuous Access (CA) technology on XP storage products. • Clusters with no shared disks-Some specialized configurations exist that need tightly consistent cluster features without having shared disks. For example: - Clusters that host applications that can failover, but where there is some other, application-specific way to keep data consistent between nodes (for example, database log shipping for keeping database state up-to-date; file replication for relatively static data, etc.). - Clusters that host applications having no persistent data, but need to cooperate in a tightly coupled way to provide consistent volatile state. - Independent Software Vendors: by abstracting storage from the Cluster Service, it provides independent software vendors with much greater flexibility in how they design sophisticated cluster scenarios. Heartbeats Heartbeats are network packets periodically broadcast by each node over the private network of the cluster. Their purpose is to inform other nodes of its health, configuration, and network connection status. When heartbeat messages are not received among the other nodes as expected, the Cluster service interprets it as node failure, and a failover is initiated. Virtual servers Groups that contain an IP address resource and a network name resource (along with other resources) are published to clients on the network under a unique server name. Because these groups appear as individual servers to clients, they are called virtual servers. Users access applications or services on a virtual server in the same way they would if the application or service were on a physical server. They do not even need to know that they are connecting to a cluster and have no knowledge of which node they are really connected to. Failover Failover is the process of moving a group of resources from one node to another in the case of a failure. For example, in a cluster where Microsoft Internet Information Server (IIS) is running on node A and node A fails, IIS will failover to node B of the cluster. 17