Volume Replicator maintains a block-level consistency between a Primary volume and the corresponding Secondary volumes. Applications that are built on Storage Foundation volumes, such as a file system, require a higher level of consistency. To support this higher-level consistency model, the Volume Replicator provides the IBC messaging facility.

The IBC messaging facility allows applications to insert control messages into a Replicated Volume Group's (RVG) update stream. This control message is application-defined and is completely transparent to the replication process. The IBC messages follow the same consistency rules as updates to a volume. When you send the IBC messages, if you ensure that it is sent when there is no major concurrent activity then it is sent in the same sequence as it was issued. If it is sent while there is concurrent activity, the message is delivered arbitrarily in relation to the activity.

The administrators at the Primary and Secondary hosts decide the protocol that the Primary uses to specify the message and the Secondary to understand that message.