The Voting Disk provides an additional communication path for the cluster nodes in case of problems with the Interconnect. It prevents Split-Brain scenarios. That is another topic from my recent course Oracle Grid Infrastructure 11g: Manage Clusterware and ASM that I’d like to share with the Oracle Community.
Under normal circumstances, the cluster nodes are able to communicate through the Interconnect. Not only do the cssd background processes interchange a network heartbeat that way, but also things like Cache Fusion are done on that path. The red lines in the picture symbolize the cssd network heartbeat. Additionally, the cssd processes write also into the Voting Disk (respectively Voting File) regularly and interchange a disk heartbeat over that path. The blue lines in the picture stand for that path. Each cssd makes an entry for its node and for the other nodes it can reach over the network:
Now in case of a network error, a Split-Brain problem would occur – without a Voting Disk. Suppose node1 has lost the network connection to the Interconnect. In order to prevent that, redundant network cards are recommended since a long time. We introduced HAIP in 184.108.40.206 to make that easier to implement, without the need of bonding, by the way. But here, node1 cannot use the Interconnect anymore. It can still access the Voting Disk, though. Nodes 2 and 3 see their heartbeats still but no longer node1, which is indicated by the green Vs and red fs in the picture. The node with the network problem gets evicted by placing the Poison Pill into the Voting File for node1. cssd of node1 will commit suicide now and leave the cluster:
Related posting: Voting Disk and OCR in 11gR2: Some changes