6.1.1 PNM Fault Monitoring and Failover

PNM monitors the state of the public network and the network adapters associated with each node in the cluster, and reports dubious or errored states. When PNM detects lack of response from a primary adapter (the adapter currently carrying network traffic to and from the node) it fails over the network service to another working adapter in the adapter backup group for that node. PNM then performs some checks to determine whether the fault is with the adapter or the network.

If the adapter is faulty, PNM sends error messages to syslog(3), which are in turn detected by the Cluster Manager and displayed to the user through a GUI. After a failed adapter is fixed, it is automatically tested and reinstated in the backup group at the next cluster reconfiguration. If the entire adapter backup group is down, then the Sun Cluster framework invokes a failover of the node to retain availability. If an error occurs outside of PNM's control, such as the failure of a whole subnet, then a normal failover and cluster reconfiguration will occur.

PNM monitoring runs in two modes, cluster-aware and cluster-unaware. PNM runs in cluster-aware mode when the cluster is operational. It uses the Cluster Configuration Database (CCD) to monitor status of the network. For more information on the CCD, see the overview chapter in the Sun Cluster 2.2 Software Installation Guide. PNM uses the CCD to distinguish between public network failure and local adapter failure. See "C.3 Sun Cluster Fault Probes" for more information on logical host failover initiated by public network failure.

PNM runs in cluster-unaware mode when the cluster is not operational. In this mode, PNM is unable to use the CCD and therefore cannot distinguish between adapter and network failure. In cluster-unaware mode, PNM simply detects a problem with the local network connection.

You can check the status of the public network and adapters with the PNM monitoring command, pnmstat(1M). See the man page for details.