To provide high availability, the cluster must be capable of taking corrective action when a node fails. In this situation, VCS configures its components to reflect the altered membership.
Problems arise when the mechanism that detects the failure breaks down because symptoms appear identical to those of a failed node. For example, if a system in a two-node cluster fails, the system stops sending heartbeats over the private interconnects and the remaining node takes corrective action. However, the failure of private interconnects (instead of the actual nodes) would present identical symptoms and cause each node to determine its peer has departed. This situation typically results in data corruption because both nodes attempt to take control of data storage in an uncoordinated manner.
In addition to a broken set of private networks, other scenarios can generate this situation. If a system is so busy that it appears to stop responding or "hang," the other nodes could declare it as dead. This declaration may also occur for nodes using hardware that supports a "break" and "resume" function. When a node drops to PROM level with a break and subsequently resumes operations, the other nodes may declare the system dead even though the system later returns and begins write operations.
VCS uses a technology called I/O fencing to remove the risk associated with split brain. I/O fencing allows write access for members of the active cluster and blocks access to storage from non-members; even a node that is alive is unable to cause damage.