HP Integrity rx5670 Windows Integrity Cluster Installation and Configuration G - Page 15

Figure 1-2 Introduction Cluster terminology The following is a sample diagram of a single quorum in a four-node cluster: Single quorum example Single quorums are sufficient for the majority of situations that most users encounter. Typical situations include: • Highly available data in a single location-Most customers that require their data to be highly available only need this on a per site basis. If they have multiple sites, each site has its own cluster. Typical applications that use this type of cluster include Microsoft SQL Server, file shares, printer queues, and network services (for example, DHCP & WINS). • Stateful applications-Applications or Windows NT services that require only a single instance at any time and require some sort of state to be stored, typically use single quorums, as they already have some sort of shared storage for maintaining the state. Connecting all nodes to a single storage device simplifies the challenge of transferring control of the data to a backup node. Another advantage to this type is that only one node needs to remain active in order for the cluster to continue to function. However, this architecture does have several weaknesses. If the storage device fails, the entire cluster fails. If the storage area network (SAN) fails, the entire cluster fails. And while the storage device and SAN can be designed with complete redundancy to eliminate those possibilities, there is one component in this architecture that can never be truly redundant - the facility itself. Floods, fires, earthquakes, extended power failures, and other serious problems will cause the entire cluster to fail. If your business continuity requirements require that work continue even if the facility is taken offline, a single quorum cluster solution alone will not meet your needs. Chapter 1 15