Whenever the cluster cannot determine who owns the quorum, challenge defense is initiated.
Eachnode in the cluster renews the disk reservation that it owns, including the quorum disk, every three seconds. If the nodes of a cluster lose network communication with each other (for example, if there is no communication over the private or public network), the Cluster service (by using Clusdisk.sys) begins using the Challenge/Defense protocol. The Challenge/Defense protocol is the cluster node functionality that determines which nodes own the shared disks and which nodes are online and functioning. The Challenge/Defense protocol uses the SCSI commands for this functionality. The following procedure describes what occurs if the nodes in a cluster lose network connectivity and there is no available network for eartbeat communications:
1. The node that currently owns the quorum disk is called the “defender.” The defender assumes that it is the only surviving node and it continually renews the quorum by issuing a scsi reserve command every three seconds.
2. All other nodes (nodes that do not own the quorum disk) become the “challengers.”
3. When the challenger detects the loss of heartbeat communications, it immediately issues a bus-wide scsi reset command.
4. Ten seconds after the scsi reset command is issued, the challenger tries to reserve the quorum disk.
· If the defender node is online and functioning, it will have already reserved the quorum disk as it typically does every three seconds. The challenger detects that it cannot reserve the quorum, and then shuts down its Cluster service.
· If the defender is not functioning properly, the challenger can successfully reserve the quorum disk. After ten seconds, the challenger brings the quorum online and takes ownership of all resources in the cluster.