Efficient content distribution in large networks comprising datacenters, end hosts, and distributed in-network caches is a difficult problem. Existing systems rely on mechanisms and metrics that fail to effectively utilize all available sources of bandwidth in the network. This paper presents a novel metric, called the Content Propagation Metric (CPM), for quantitatively evaluating the marginal benefit of available bandwidth to competing consumers, enabling efficient utilization of the bandwidth resource. The metric is simple to implement, imposes only a modest overhead, and can be retrofitted easily into existing content distribution systems. We have designed and implemented a high-performance content distribution system, called V-Formation, based on the CPM. The CPM guides V-Formation toward a global allocation of bandwidth that maximizes the aggregate download bandwidth of consumers. Results from a PlanetLab deployment and extensive simulations show that V-Formation achieves high aggregate bandwidth and that the CPM enables hosts to converge quickly on a stable allocation of resources in a wide range of deployment scenarios.

The task of consistently and reliably replicating data is fundamental in distributed systems, and numerous existing protocols are able to achieve such replication efficiently. When called on to build a large-scale enterprise storage system with built-in replication, we were therefore surprised to discover that no existing protocols met our requirements. As a result, we designed and deployed a new replication protocol called Niobe . Niobe is in the primary-backup family of protocols, and shares many similarities with other protocols in this family. But we believe Niobe is significantly more practical for large-scale enterprise storage than previously published protocols. In particular, Niobe is simple, flexible, has rigorously proven yet simply stated consistency guarantees, and exhibits excellent performance. Niobe has been deployed as the backend for a commercial Internet service; its consistency properties have been proved formally from first principles, and further verified using the TLA + specification language. We describe the protocol itself, the system built to deploy it, and some of our experiences in doing so.