This section outlines the steps necessary to prevent Pacemaker from promoting a drbd Master/Slave resource when its DRBD replication link has been interrupted. This keeps Pacemaker from starting a service with outdated data and causing an unwanted “time warp” in the process.

	Important
	It is absolutely vital to configure at least two independent OpenAIS communication channels for this functionality to work correctly. Furthermore, as mentioned in the section called “Adding a DRBD-backed service to the cluster configuration”, you should make sure the DRBD init script is disabled.

In order to enable resource-level fencing for Pacemaker, you will have to set two options in drbd.conf:

resource resource {
  disk {
    fencing resource-only;
    ...
  }
  handlers {
    fence-peer "/usr/lib/drbd/crm-fence-peer.sh";
    after-resync-target "/usr/lib/drbd/crm-unfence-peer.sh";
    ...
  }
  ...
}

Thus, if the DRBD replication link becomes disconnected, the crm-fence-peer.sh script contacts the cluster manager, determines the Pacemaker Master/Slave resource associated with this DRBD resource, and ensures that the Master/Slave resource no longer gets promoted on any node other than the currently active one. Conversely, when the connection is re-established and DRBD completes its synchronization process, then that constraint is removed and the cluster manager is free to promote the resource on any node again.