and control messages so that the Cluster Manager has accurate information about the status of its partner.
When a cluster becomes partitioned, and the network problem is cleared after the point when takeover processing has begun so that keepalive packets start flowing between the partitioned nodes again, something must be done to restore order in the cluster. This order is restored by the DGSP Message.
7.5 The DGSP Message
A DGSP message (short for Diagnostic Group Shutdown Partition) is sent when a node loses communication with the cluster and then tries to
For example, if a cluster node becomes unable to communicate with other nodes, yet it continues to work through its process table, the other nodes conclude that the “missing” node has failed because they no longer are receiving keepalive messages from it. The remaining nodes then process the necessary events to acquire the disks, IP addresses, and other resources from the “missing” node. This attempt to take over resources results in the
As the disks are being acquired by the takeover node (or after the disks have been acquired and applications are running), the “missing” node completes its process table (or clears an application problem) and attempts to resend keepalive messages and rejoin the cluster. Since the disks and IP addresses are in the process of being successfully taken over, it becomes possible to have a duplicate IP address on the network and the disks may start to experience extraneous traffic on the data bus.
Because the reason for the “missing” node remains undetermined, you can assume that the problem may repeat itself later, causing additional down time of not only the node but also the cluster and its applications. Thus, to ensure the highest cluster availability, a DGSP message is sent to all nodes in one of the partitions. Any node receiving a DGSP message halts immediately, in order to not cause any damage on disks or confusion on the networks.
In a partitioned cluster situation, the smaller partition (lesser number of nodes) is shut down, with each of its nodes getting a DGSP message. If the partitions are of equal size, the one with the node name beginning in the lowest name in the alphabet gets shut down. For example, in a cluster where one partition has NodeA and the other has NodeB, NodeB will be shut down.
