In Windows Server 2003, the Quorum disk resource is required for the Cluster to function. In your example, if the Quorum disk suddenly became unavailable to the cluster then both nodes would immediately fail and not be able to restart the clussvc.
In that light, the Quorum disk was a single point of failure in a Microsoft Cluster implementation. However, it was usually a fairly quick workaround to get the cluster back up and operational. There are generally two solutions to that type of problem.
1. Detemrine why the Quorum disk failed and repair.
2. Reprovision a new LUN, present it to the cluster, assign it a drive letter and format.
Then start one node with the /FQ switch and through cluadmin designate the new disk resource as the Quorum.
Then stop and restart the clussvc normally and then bring online the second node.
What happens to a running Cluster if the quorum disk fails in Windows Server 2008 Cluster?
Cluster continues to work but failover will not happen in case of any other failure in the active node.
