Sun Cluster 3.1 Concepts Guide

Cluster Membership Monitor

The Cluster Membership Monitor (CMM) is a distributed set of agents, one per cluster member. The agents exchange messages over the cluster interconnect to:

Unlike previous Sun Cluster software releases, CMM runs entirely in the kernel.

Cluster Membership

The main function of the CMM is to establish cluster-wide agreement on the set of nodes that participates in the cluster at any given time. This constraint is called the cluster membership.

To determine cluster membership, and ultimately, ensure data integrity, the CMM:

See Quorum and Quorum Devices for more information on how the cluster protects itself from partitioning into multiple separate clusters.

Cluster Membership Monitor Reconfiguration

To ensure that data is kept safe from corruption, all nodes must reach a consistent agreement on the cluster membership. When necessary, the CMM coordinates a cluster reconfiguration of cluster services (applications) in response to a failure.

The CMM receives information about connectivity to other nodes from the cluster transport layer. The CMM uses the cluster interconnect to exchange state information during a reconfiguration.

After detecting a change in cluster membership, the CMM performs a synchronized configuration of the cluster, where cluster resources might be redistributed based on the new membership of the cluster.

Failfast Mechanism

If the CMM detects a critical problem with a node, it calls upon the cluster framework to forcibly shut down (panic) the node and to remove it from the cluster membership. The mechanism by which this occurs is called failfast. Failfast will cause a node to shut down in two ways.

When a node panics due to the death of a cluster daemon, a message similar to the following will display on the console for that node.

panic[cpu0]/thread=40e60: Failfast: Aborting because "pmfd" died 35 seconds ago.
409b8 cl_runtime:__0FZsc_syslog_msg_log_no_argsPviTCPCcTB+48 (70f900, 30, 70df54, 407acc, 0)
%l0-7: 1006c80 000000a 000000a 10093bc 406d3c80 7110340 0000000 4001 fbf0

After the panic, the node might reboot and attempt to rejoin the cluster or stay at the OpenBootTM PROM (OBP) prompt. The action taken is determined by the setting of the auto-boot? parameter in the OBP.