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Quorum is an important concept to understand in clustering. For a cluster to be active, it needs some method of keeping track of which node is the current owner of the cluster object. How this is achieved depends on the number of nodes that will be in your cluster. If you have an odd number of nodes, the default quorum configuration Node Majority will work just fine. If you have an even number of nodes, quorum configuration Node and Disk Majority should be used.
For a cluster to be up, it has to have quorum. Quorum can only be achieved when greater than 50% of the quorum members are actively participating.
- Let’s say you have only two nodes. With Node Majority, when both servers are active, everything will work fine. But as soon as one server goes offline, the percentage of participants is not greater than 50% and the cluster will then become unavailable.
In contrast, what if you have three nodes? In that case, if one host is down, you still would have 66% of the participants and the cluster is still available.
Node and Disk Majority - Let’s make the same comparison as before. In a two node cluster, when one host goes down, you still have one host and the disk participant so you still have 66% of the participants.
What about three nodes and the added disk participant? Having the disk participate here is not necessary. With the loss of one node, the other two nodes are still providing 66%.
The overall purpose of quorum is to maintain availability of the cluster even when half the nodes are offline. For further quorum documentation seeUnderstandingQuorumConfigurationinaFailoverCluster and AppendixA: DetailsofHowQuorumWorksinaFailoverCluster..
Now you need to get the disks connected to your host. Use an iSCSI intiator to connect to the SAN iSCSI targets. Windows Server 2008 and later includes iSCSI Initiator. Network cards that include iSCSI offloading may have their own connection client. Your list of connections should also include any CSV disks.
In Windows Server 2008 R2, the iSCSI Initiator allows you to quickly connect to the virtual disks on the SAN by typing in the IP address of the SAN and clicking Quick Connect. This will display a list of targets and allow you to select each one and click Connect.
Adding IP to host - iSCSI Initiator connection for csv1 and vmquorum
With targets connected, the disks will display in Disk Management as offline. The disk that will be used for quorum can now be brought online and assigned a drive letter. Any disks that will be used as cluster shared volumes should be formatted but should not be assigned a drive letter or mount point. This is important to be aware of as it is a requirement for a CSV. In my example, I have a 256MB disk with drive letter Q for my quorum. I have another 100GB disk that I’ll use as a cluster shared volume.
Cluster Shared Volume 1 and Quorum disk for Hyper-V host cluster
This post covered the two different quorum types that you should use in Hyper-V clustering. Setting up your disks was also covered. The next post in this series will be covering the creation and configuration of your cluster and the cluster shared volume.