I/O Fencing is a base part of Veritas Cluster Server focused on properly handling a cluster partition event or the loss of cluster communication. I/O Fencing consists of two distinct components, Membership Arbitration and Data Protection; together they are able to deliver maximum data *integrity* in a cluster environment --so you can be rest assured that no two cluster partitions will write to the shared disks in an uncoordinated manner (in the event of a cluster partition). It does not intended to recover/re-route inflight/stale IOs from clients. I hope that clarifies. For additional details on fencing with VCS, please see:
https://www-secure.symantec.com/connect/articles/veritas-cluster-server-io-fencing-deployment-considerations