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
re-establish communication.
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
dual-attached disks receiving resets to release them from the “missing” node
and the start of IP address takeover scripts.
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.
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