How to change the quorum disk designation

This article explains the quorum disk resource in Windows Clustering, and describes how to change the drive for the quorum device.

In the event of failure, Windows Clustering maintains a primary node, and replicates changes for the cluster registry by means of a shared disk. This disk is called the quorum drive. The quorum drive has two responsibilities:

• It replicates the cluster registry to all other nodes in the server cluster. The cluster registry is stored in the following location on each node:
  %SystemRoot%\Cluster\Clusdb
  The cluster registry is replicated to the \Mscs\Chkxxx.tmp file on the quorum drive. These files are exact copies of each other and can be manually copied and renamed to replace each other. The Quolog.log file is a transaction log that maintains a record of all changes to the checkpoint file so that these changes can be appended to nodes that were offline when they join back into the cluster. Quolog.log is stored in the \Mscs directory on the quorum disk.
• If there is a loss of communication between the nodes in the cluster, a "Split Brain" scenario occurs. In this situation, the owner of the quorum disk resource becomes the only owner of the cluster and all the resources. The owner then makes the resources available for clients. When the node that owns the quorum disk does not function correctly, the surviving nodes arbitrate to take ownership of the device. In a single cluster, there is a local quorum resource. In the event of a hardware failure of the quorum disk, it may be necessary to designate another device as the quorum disk.

The quorum disk is located on a shared bus in the cluster. Use the following procedure to designate a different drive for the quorum device:

1. Start Cluster Administrator (CluAdmin.exe).
2. Right-click the cluster name in the upper-left corner, and then click Properties.
3. Click the Quorum tab.
4. In the Quorum resource box, click a different disk resource.
5. If the disk has more than one partition, click the partition where you want the cluster-specific data to be kept, and then click OK.

NOTE: If you cannot start Cluster service because the quorum disk is unavailable, use the /FIXQUORUM switch to start Cluster service. You are then able to change the quorum disk designation.

When you change the quorum disk designation, Cluster service does not remove the /Mscs directory from the old drive. For administrative purposes, you may want to delete this old directory, or keep it as a backup. Do not continue running Cluster service with the /FIXQUORUM switch enabled. When the new quorum disk is established, stop the service and restart it without a switch. Then it is safe to bring other nodes online.

It is recommended that you increase the quorum log size to 4,096 KB.

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