I/O Fencing is a feature that prevents data corruption in the event of a communication breakdown in a cluster.

To provide high availability, Microsoft Failover Clustering takes corrective action when a node fails. In this situation, SFW also updates its components to reflect the altered CVM 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. The remaining node then takes corrective action. The failure of the private interconnects, instead of the actual nodes, presents identical symptoms and causes each node to determine its peer has departed. This situation typically results in data corruption because both nodes try to take control of data storage in an uncoordinated manner.

SFW uses I/O Fencing to remove the risk that is associated with split-brain. I/O Fencing allows write access for members of the active cluster and blocks access to storage from non-members.