Final answer:
The default quorum model for clusters with an even number of nodes is the Node Majority or Node and Disk Majority, designed to maintain cluster operations as long as a majority of nodes or nodes plus a shared disk can communicate.
Step-by-step explanation:
The quorum model used by default on clusters with an even number of cluster nodes is known as the Node Majority or Node and Disk Majority (depending on whether a shared disk is used). The quorum model's function is to ensure the cluster remains online as long as the number of nodes that are operational and can communicate with each other constitute a majority of the cluster. In the Node Majority model, each node gets one vote, and the cluster has a quorum if more than half of the nodes are up and can communicate. The Node and Disk Majority model adds a shared disk with a single vote to the equation, making it beneficial in scenarios with an even number of nodes.
In the case of a Node and Disk Majority, the total number of votes equals the number of nodes plus one (for the shared disk). If more than half of the total votes are available, the cluster maintains quorum and continues to function. For example, in a four-node cluster using the Node and Disk Majority model, the cluster will have a quorum as long as three votes are available – meaning at least two nodes and the disk, or three nodes if the disk is unavailable.