Manually switching a resource's role from secondary to primary (promotion) or vice versa (demotion) is done using the following commands:
drbdadm primary resource
drbdadm secondary resource
In single-primary
mode (DRBD's default), any resource can be in the
primary role on only one node at any given time while the connection state is
Connected. Thus, issuing drbdadm primary
resource on one node
while resource is still in the
primary role on the peer will result in an error.
A resource configured to allow dual-primary mode can be switched to the primary role on both nodes.