If properly configured, DRBD can detect if the replication network is congested, and suspend replication in this case. In this mode, the primary node "pulls ahead" of the secondary — temporarily going out of sync, but still leaving a consistent copy on the secondary. When more bandwidth becomes available, replication automatically resumes and a background synchronization takes place.
Suspended replication is typically enabled over links with variable bandwidth, such as wide area replication over shared connections between data centers or cloud instances.
See Section 5.12, “Configuring congestion policies and suspended replication” for details on congestion policies and suspended replication.