This is very different from the SCC model. As a result of no shared storage, a new solution had to be
created for the quorum resource. A new quorum model was added to Windows Server 2003 called
Majority Node Set (MNS) quorum with file share witness. The feature is available as a hotfix to Windows
Server 2003, or it ??™ s included in Windows Server 2003 Service Pack 2.
The file share witness (FSW) is a file share that resides on a server outside of the cluster. Typically, the
FSW is created on a Hub server. The MNS cluster requires two of the three cluster resources available for
the cluster to stay online. For example, the FSW can go offline and not affect the cluster, because both
nodes can still communicate with each other. The nodes use a heartbeat, or periodic check, to ensure the
resource is available. Similarly, one node can lose communication and the cluster will stay online as long
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as the FSW is available. If two resources cannot communicate, the entire cluster will shut down. This is
because without the heartbeat and connectivity to the FSW, the node cannot determine if it ??™ s the active
node. If both nodes think they are the active node, this condition is called split brain syndrome. Unlike in
SCC, split brain cannot occur in a CCR cluster because if there is no majority, the nodes will not come
online.
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