2.5. Automatic Promotion of Resources

Prior to DRBD 9, promoting a resource would be done with the drbdadm primary command. With DRBD 9, DRBD will automatically promote a resource to primary role when the auto-promote option is enabled, and one of its volumes is mounted or opened for writing. As soon as all volumes are unmounted or closed, the role of the resource changes back to secondary.

Automatic promotion will only succeed if the cluster state allows it (that is, if an explicit drbdadm primary command would succeed). Otherwise, mounting or opening the device fails as it did prior to DRBD 9.