Maybe a silly question, but the DRBD_INTERFACE parameter in iscsi-ha.conf should be filled with the interface that contains one of the DRBD/iSCSI IP Addresses or must be an unused host interface?
DRBD_INTERFACE should be set to the interface name of the port used for the replication network. In our how-to this would be the 10.10.10.0 network.
The parameter is used in the logic to apply/bind the floating IP address to the interface speficed here.