![]() ![]() However, if a node on another subnet is seen as non-responsive in a quorum vote, but it is actually online and otherwise healthy, that is most likely due to a network communications failure between subnets. ![]() Network communications between nodes on the same physical subnet should be considered reliable the quorum vote should be trusted. A key function of the quorum vote is to determine whether the apparent state of each of node in the WSFC cluster is indeed that actual state of those nodes.įor all of the quorum models except 'Disk Only', the effectiveness of a quorum vote depends on reliable communications between all of the voting nodes in the cluster. At any given moment, from the perspective of each node, some of the other nodes may appear to be offline, or appear to be in the process of failover, or appear unresponsive due to a network communication failure. No individual node in a WSFC cluster can definitively determine that the cluster as a whole is healthy or unhealthy. The quorum discussion to this point has carefully qualified the set of WSFC cluster nodes that vote on cluster health as voting nodes. Voting and Non-Voting Nodesīy default, each node in the WSFC cluster is included as a member of the cluster quorum each node has a single vote in determining the overall cluster health, and each node will continuously attempt to establish a quorum. When using an asymmetric storage configuration for Always On availability groups, you should generally use the Node Majority quorum mode when you have an odd number of voting nodes, or the Node and File Share Majority quorum mode when you have an even number of voting nodes. A shared disk cluster resource is designated as a witness, and connectivity by any node to that shared disk is counted as an affirmative vote. More than one-half of the possible votes must be affirmative for the cluster to be healthy.ĭisk Only. Similar to Node Majority quorum mode, except that a shared disk cluster resource is also designated as a voting witness, and connectivity from any node to that shared disk is also counted as an affirmative vote. More than one-half of the possible votes must be affirmative for the cluster to be healthy.Īs a best practice, the witness file share should not reside on any node in the cluster, and it should be visible to all nodes in the cluster. Similar to Node Majority quorum mode, except that a remote file share is also configured as a voting witness, and connectivity from any node to that share is also counted as an affirmative vote. More than one-half of the voting nodes in the cluster must vote affirmatively for the cluster to be healthy. ![]() The following quorum modes can be used to determine what constitutes a quorum of votes: ![]() The Failover Cluster Manager utility will recommend a quorum mode based on the number of nodes in the cluster. Quorum ModesĪ quorum mode is configured at the WSFC cluster level that dictates the methodology used for quorum voting. If a WSFC cluster is set offline because of quorum failure, manual intervention is required to bring it back online.įor more information, see: WSFC Disaster Recovery through Forced Quorum (SQL Server). This will also cause all SQL Server instances registered with the cluster to be stopped. If the quorum vote fails, the WSFC cluster will be set offline as a precautionary measure. Overall WSFC cluster health must be maintained in order to ensure that healthy secondary nodes are available for primary nodes to fail over to. The absence of a quorum indicates that the cluster is not healthy. The presence of a quorum means that the cluster is healthy and able to provide node-level fault tolerance. The overall health and status of a WSFC cluster is determined by a periodic quorum vote. Unresponsive nodes are considered to be in a failed state.Ī quorum node set is a majority of the voting nodes and witnesses in the WSFC cluster. Cluster Health Detection by QuorumĮach node in a WSFC cluster participates in periodic heartbeat communication to share the node's health status with the other nodes. A fundamental understanding of WSFC quorum modes and node voting configuration is very important to designing, operating, and troubleshooting your Always On high availability and disaster recovery solution. WSFC uses a quorum-based approach to monitoring overall cluster health and maximize node-level fault tolerance. Both SQL Server Always On availability groups and Always On Failover Cluster Instances (FCI) take advantage of Windows Server Failover Clustering (WSFC) as a platform technology. ![]()
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