A dynamic feedback technique improves data replication performance by balancing rates of data retrieval and data transmission of a fragmented virtual disk replicated between nodes of clusters on a local site and a remote site of a disaster recovery environment. Each node is embodied as a physical computer with hardware resources, such as processor, memory, network and storage resources, which are virtualized to provide support for one or more user virtual machines executing on the node. The storage resources include storage devices of an extent store, whereas the network includes a wide area network connecting the local and remote sites. The dynamic feedback technique employs a virtual memory buffer configured to balance the data storage retrieval and network transmission rates at a source of replication based on bandwidth demands of the extent store and network throughput as manifested by an available free space (i.e., emptiness) of the virtual buffer.