When establishing a Windows Server Failover Cluster (WSFC), a crucial element is configuring quorum options. The quorum demonstrates the number of failures that a cluster can endure and keep working. This is an important topic within the DP-300 Administering Microsoft Azure SQL Solutions exam.
For a WSFC, you need over half of all the votes to conduct administrative tasks, ensure synchronization, and assume the control of clustered roles. The key thing to comprehend is that a quorum enables you to evade split-brain scenarios, where network partitions occur and two separate clusters believe they are fully-functional and thus controlling.
Quorum Configuration Options
WSFC offers four quorum configuration options:
- Node Majority: Every cluster node has a vote. In this mode, the cluster can endure failures of a minority of nodes.
- Node and Disk Majority: Each cluster node plus a designated disk witness, generally a small portion of the cluster shared volume, have a vote. The cluster can then survive failures of half the nodes (rounding down), plus one.
- Node and File Share Majority: Each cluster node, and a file share witness also have votes. This configuration is suitable for even number of nodes and the cluster can endure failures of half the nodes.
- No Majority: Disk Only: Only the designated disk retains a vote. This model should only be used as a last resort.
Let’s take a deeper view of each.
Node Majority
In a node-majority cluster, only nodes have a vote. This configuration is typically used in clusters with an odd number of nodes. The cluster can endure failure of less than half the nodes.
For example, consider a three-node cluster, where each node has a vote. Two votes forms the majority. So, the cluster can survive one node failure, but if two nodes fail, the remaining node will not have a quorum, and thus the cluster will fail.
Node and Disk Majority
Here, each node and a disk witness have a vote. This configuration works with an even number of nodes, and the cluster can endure the failures of half the enabled nodes (rounding down to the nearest whole number), plus one.
For instance, in a four-node cluster, each node and the disk witness have a vote. Therefore, the majority is three votes. The cluster can survive a failure of two nodes or one node and a disk witness.
Node and File Share Majority
Each cluster node and a file share witness have votes in this configuration. Like the Node and Disk Majority option, it’s oriented towards an even number of nodes, and the cluster can survive the failures of half the nodes.
Consider a four-node cluster, each node and the file share witness have a vote, meaning a majority is three votes. The cluster can endure the failure of two nodes or one node and the file share witness.
No Majority: Disk Only
The least recommended quorum option, where only the disk has a vote. This configuration keeps the cluster running as long as the disk witness is available, even if all nodes fail. This should be used as a last resort when other quorum configurations fail.
Conclusion
Configuring quorum options for WSFC is essential for the efficient running and high availability of your cluster. By understanding each quorum, their benefits, and their limitations, you’re better equipped to determine the correct quorum for your cluster, essentially a key component to managing Azure SQL Solutions as covered in the DP-300 Microsoft certification exam.
Practice Test
True or False: A “Quorum” in a Windows Server Failover Cluster refers to the minimum number of voters that must be online to sustain cluster operations.
- 1) True
- 2) False
Answer: True
Explanation: The Quorum in Windows Cluster Services determines the number of failures that the cluster can sustain while still remaining online.
A quorum configuration with “Node Majority” means that each node in a cluster has a vote and the majority of those votes decides whether to start a cluster.
- 1) True
- 2) False
Answer: True
Explanation: In a Node Majority quorum configuration, each node has one vote, and the cluster remains running as long as a majority of the nodes are online.
True or False: quorum configurations for a Windows server failover cluster can be done manually or through automated tools.
- 1) True
- 2) False
Answer: True
Explanation: Both manual and automated configurations are possible for a failover cluster quorum.
What is “Node and Disk Majority” in quorum configuration?
- 1) A quorum configuration where each node and the disk has a vote.
- 2) A quorum configuration where only the node has a vote, not the disk.
- 3) A quorum configuration with no node voters.
Answer: A quorum configuration where each node and the disk have a vote.
Explanation: In Node and Disk Majority, every node and a specified disk witness have a vote.
True or False: In “Node and File Share Majority”, a file share is designated as a witness and can vote.
- 1) True
- 2) False
Answer: True
Explanation: In this quorum configuration, a file share can act as a witness that has a vote in the cluster.
The Node and Cloud Witness is a quorum configuration option enabled in:
- 1) Windows Server 2008
- 2) Windows Server 2012
- 3) Windows Server 2016
- 4) Windows Server 2000
Answer: Windows Server 2016
Explanation: The Node and Cloud Witness configuration is a newer option, made available in Windows Server
True or False: Dynamic Quorum adjusts the vote allocation dynamically as the cluster membership changes.
- 1) True
- 2) False
Answer: True
Explanation: As the cluster membership changes, Dynamic Quorum reallocates the vote, which helps to sustain the service availability in the time of a node failure.
If there is an even number of nodes without any additional witness, the Node Majority quorum configuration can face issues.
- 1) True
- 2) False
Answer: True
Explanation: Without the witness vote, an equal number of nodes might not reach a majority agreement, potentially causing a split-brain situation.
True or False: Quorum is essential to avoid the “split-brain” condition in a cluster.
- 1) True
- 2) False
Answer: True
Explanation: Quorum is critical to avoid “split-brain” scenarios where multiple subsets of nodes think they are active, resulting in data corruption or loss.
The No Majority option in quorum configuration:
- 1) Is not recommended for production use.
- 2) Is recommended for production use.
- 3) Is the preferred option in Windows Server
Answer: Is not recommended for production use.
Explanation: The “No Majority” option, while available, is generally not recommended for production use as it does not prevent the split-brain scenario.
Interview Questions
How many nodes are necessary for creating a Windows Server Failover Cluster?
At least two nodes are necessary for creating a Windows Server Failover Cluster.
Which quorum configuration would be suitable for a three-node failover cluster?
The Node Majority quorum configuration would be suitable for a three-node failover cluster.
What is the role of a witness in a Windows Server Failover Cluster’s quorum configuration?
A witness provides an additional vote in the quorum configuration of a Windows Server Failover Cluster and helps to maintain a majority of votes.
Can you explain the Node and Disk Majority quorum configuration for a Windows Server Failover Cluster?
In the Node and Disk Majority configuration, each node and disk in the cluster has a vote, and the cluster functions as long as the majority of votes are online. It is good for clusters with an even number of nodes.
What is the main benefit of a Node Majority configuration in a Windows Server Failover Cluster?
The main benefit of a Node Majority configuration is that it allows the cluster to continue operation as long as the majority of nodes are online.
What is the Dynamic Quorum in the context of Windows Server Failover Clusters?
Dynamic Quorum dynamically adjusts the vote majority based on the number of voting nodes that are operating at a given time. This helps to keep the cluster operational even if more than half of the nodes fail.
In what scenario would a No Majority: Disk Only configuration be used?
A No Majority: Disk Only configuration is typically used in clusters with a single point of failure, such as a single shared storage.
What is a quorum witness?
A quorum witness is a designated disk or file share that holds a copy of the cluster database and can provide an additional vote when it comes to deciding whether to keep the cluster in operation.
How many nodes are needed in a cluster for Node Majority (no witness) quorum configuration?
A Node Majority (no witness) quorum configuration is recommended for clusters with an odd number of nodes.
What happens when there is a loss of communication between the nodes in a cluster configured with a Node Majority quorum?
If the nodes in a cluster lose communication with each other, the cluster will continue to function only if the majority of the nodes are still communicating with each other. If less than half of the nodes are communicating, the entire cluster will go offline.
Can a quorum configuration be changed after the creation of a cluster?
Yes, the quorum configuration can be changed after the creation of a cluster using the Configure Cluster Quorum Wizard in the Failover Cluster Manager.
What role does the quorum play in the failover process of a Windows Server Failover Cluster?
The quorum in a Windows Server Failover Cluster determines the number of failures that the cluster can tolerate while still remaining online. If too many failures occur, the cluster will stop running.
Can a file share witness be used in a Windows Server Failover Cluster without shared storage?
Yes, a file share witness can be used in a Windows Server Failover Cluster without shared storage.
How does a cloud witness work in a Windows Server Failover Cluster?
A cloud witness acts as a vote in a quorum for a Windows Server Failover Cluster. It leverages the Azure Blob Storage service to read/write a small amount of data to an Azure Storage Account.
What is the role of the Dynamic Witness in a Windows Server Failover Cluster?
The Dynamic Witness helps in balancing the votes for a Windows Server Failover Cluster. If there’s an odd number of votes, the witness doesn’t have a vote. But if there’s an even number, the witness has a vote. This ensures that the total number of votes is always odd, maintaining the stability of the server cluster.
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