Different types of Failover Server Clusters - Single-Quorum Cluster, Single Local Quorum and Majority Node Set (MNS)

The following are the three main types of failover server clusters can be created using Windows Server 2003 Operating System.

Single-Quorum Cluster

A Single-Quorum Cluster is a multi-server configuration with a quorum stored on a disk attached to a storage bus (SCSI or Fibre), shared among all the nodes. The Single shared quorum cluster model has two or more nodes and all are connected to a shared storage device. In Single shared quorum model, only one copy of the quorum data is maintained and is housed on the shared storage device. All cluster nodes have access to the quorum data, but the quorum disk resource runs only on one node of the cluster at a time.

Single Local Quorum

A Single local quorum is a single-server configuration with a quorum stored on the server’s local disk. The single-node cluster can use the local quorum resource which is kept on the local hard disk storage. The local quorum resource is used only for cluster application development and testing of cluster applications.

The main disadvantage of single-node cluster is that since there is only one node, the cluster will not provide failover. If the single node is down, all the cluster groups are unavailable.

Majority Nodes Set (MNS)

A Majority Nodes Set (MNS) is a multi-server configuration with or without a shared storage bus and a quorum distributed across the entire server.

In a Majority Node Set (MNS) cluster, each node keeps a local copy of the quorum device data. Windows Server 2003 Enterprise supports up to four nodes per cluster, and Datacenter supports up to eight nodes. Since each node in a Majority Node Set (MNS) cluster maintains a local copy of the quorum, the shared storage device is not necessary and the Majority Node Set (MNS) clusters can be deployed across a WAN in a geographically distributed environment.