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Types of Server Clustering

There are three main types of server clusters. These three types of servers are called nodes and are connected to the devices that store the cluster configuration and state data. This data is stored in such a way that allows each active node to obtain the data even if one or more of the nodes are down.

This stored data is kept on a resource known as the quorum resource. The data stored on the quorum resource includes cluster configuration information plus records (often referred to as checkpoints) these represent the most recent changes made to that configuration. Any nodes that comes online after an outage will use the quorum resource as the definitive source for recent changes in the clusters' configuration.

The 3 main types of server clusters are:

  • Single quorum device cluster, also called a standard quorum cluster
  • Majority node set cluster
  • Local quorum cluster, also called a single node cluster.

Single quorum device cluster

The most common form of server clustering is the single quorum device cluster - which is often called the standard quorum cluster. this this type of cluster has multiple nodes which are connected to cluster storage and a connectection device which acts as the bus. Each disk in the cluster storage array is owned and managed by one server at a time, it is the disk array that contains the quorum resource.

Majority node set cluster

A second type of cluster is the majority node set cluster, each node maintains a copy of the cluster configuation data and the quorum resource keeps the configuration consistent throughout the nodes. The majority node set clusters can for this reason be used for geographically dispersed clusters. A major advantage of this form of clustering is that the quorum resource can be easily taken offline for maintenance and the cluster will continue to function.

The main difference between the above cluster types is that the single quorum device clusters can operate with just one node, whereas the majority set cluster cannot.

Local quorum cluster

A local quorum cluster, which is also known as a single node cluster, only has a single node and is normally used for testing.

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