In Windows Server 2003 cluster, the quorum resource could become the single point of failure as nodes could not function if they can not communicate to the quorum resource. This limit has been removed in Windows Server 2008 cluster, as now it supports 4 quorum modes which are enabled by the newly added ‘Voting Algorithm’.
The four quorum modes:
- Node Majority: Each node that is available and in communication can vote. The cluster functions only with a majority of the votes, that is, more than half.
- Node and Disk Majority: Each node plus a designated disk in the cluster storage (the “disk witness”) can vote, whenever they are available and in communication. The cluster functions only with a majority of the votes, that is, more than half.
- Node and File Share Majority: Each node plus a designated file share created by the administrator (the “file share witness”) can vote, whenever they are available and in communication. The cluster functions only with a majority of the votes, that is, more than half.
- No Majority: Disk Only: The cluster has quorum if one node is available and in communication with a specific disk in the cluster storage. Only the nodes that are also in communication with that disk can join the cluster.
The recommended settings:
| Description of cluster | Quorum recommendation |
| Odd number of nodes | Node Majority |
| Even number of nodes (but not a multi-site cluster) | Node and Disk Majority |
| Even number of nodes, multi-site cluster | Node and File Share Majority |
| Even number of nodes, no shared storage | Node and File Share Majority |
| Exchange CCR cluster (two nodes) | Node and File Share Majority |
Reference: http://technet.microsoft.com/en-us/library/cc770620%28WS.10%29.aspx
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