Both private networks fail.

Node A races for majority of coordination points.

If Node A wins race for coordination points, Node A ejects Node B from the shared disks and continues.

Node B races for majority of coordination points.

If Node B loses the race for the coordination points, Node B panics and removes itself from the cluster.

When Node B is ejected from cluster, repair the private networks before attempting to bring Node B back.

Both private networks function again after event above.

Node A continues to work.

Node B has crashed. It cannot start the database since it is unable to write to the data disks.

Restart Node B after private networks are restored.

One private network fails.

Node A prints message about an IOFENCE on the console but continues.

Node B prints message about an IOFENCE on the console but continues.

Repair private network. After network is repaired, both nodes automatically use it.

Node A hangs.

Node A is extremely busy for some reason or is in the kernel debugger.

When Node A is no longer hung or in the kernel debugger, any queued writes to the data disks fail because Node A is ejected. When Node A receives message from GAB about being ejected, it panics and removes itself from the cluster.

Node B loses heartbeats with Node A, and races for a majority of coordination points.

Node B wins race for coordination points and ejects Node A from shared data disks.

Repair or debug the node that hangs and reboot the node to rejoin the cluster.

Nodes A and B and private networks lose power. Coordination points and data disks retain power.

Power returns to nodes and they restart, but private networks still have no power.

Node A restarts and I/O fencing driver (vxfen) detects Node B is registered with coordination points. The driver does not see Node B listed as member of cluster because private networks are down. This causes the I/O fencing device driver to prevent Node A from joining the cluster. Node A console displays:

Potentially a 
preexisting 
split brain. 
Dropping out 
of the cluster. 
Refer to the 
user 
documentation 
for steps 
required
to clear 
preexisting 
split brain.

Node B restarts and I/O fencing driver (vxfen) detects Node A is registered with coordination points. The driver does not see Node A listed as member of cluster because private networks are down. This causes the I/O fencing device driver to prevent Node B from joining the cluster. Node B console displays:

Potentially a 
preexisting 
split brain. 
Dropping out 
of the cluster. 
Refer to the 
user 
documentation 
for steps 
required
to clear 
preexisting 
split brain.

Resolve preexisting split-brain condition.

See Fencing startup reports preexisting split-brain.

Node A crashes while Node B is down. Node B comes up and Node A is still down.

Node A is crashed.

Node B restarts and detects Node A is registered with the coordination points. The driver does not see Node A listed as member of the cluster. The I/O fencing device driver prints message on console:

Potentially a 
preexisting 
split brain. 
Dropping out 
of the cluster. 
Refer to the 
user 
documentation 
for steps 
required
to clear 
preexisting 
split brain.

Resolve preexisting split-brain condition.

See Fencing startup reports preexisting split-brain.

The disk array containing two of the three coordination points is powered off.

No node leaves the cluster membership

Node A continues to operate as long as no nodes leave the cluster.

Node B continues to operate as long as no nodes leave the cluster.

Power on the failed disk array so that subsequent network partition does not cause cluster shutdown, or replace coordination points.

See Replacing I/O fencing coordinator disks when the cluster is online.

The disk array containing two of the three coordination points is powered off.

Node B gracefully leaves the cluster and the disk array is still powered off. Leaving gracefully implies a clean shutdown so that vxfen is properly unconfigured.

Node A continues to operate in the cluster.

Node B has left the cluster.

Power on the failed disk array so that subsequent network partition does not cause cluster shutdown, or replace coordination points.

See Replacing I/O fencing coordinator disks when the cluster is online.

The disk array containing two of the three coordination points is powered off.

Node B abruptly crashes or a network partition occurs between node A and node B, and the disk array is still powered off.

Node A races for a majority of coordination points. Node A fails because only one of the three coordination points is available. Node A panics and removes itself from the cluster.

Node B has left cluster due to crash or network partition.

Power on the failed disk array and restart I/O fencing driver to enable Node A to register with all coordination points, or replace coordination points.

See Replacing defective disks when the cluster is offline.