In this paper, we explore the design space and practice of a new peer-to-peer (P2P) storage cloud, which is capable of replicating, refreshing and on-demand streaming of cinematic-quality video streams, in a decentralized fashion using local storage spaces of end users. We identify key design challenges and tradeoffs in such a P2P storage cloud, and how these are addressed by making informed design choices in a step-by-step fashion. Following our design choices, we have implemented a real-world Video-on-Demand (VoD) system with over 100,000 lines of code, called Novasky, which features new coding-aware peer storage replacement and server push-to-peer strategies, in order to maintain media availability and to balance the system-wide supply-demand relationship in the P2P storage cloud. Since September 2009, it has been deployed in the Tsinghua University campus network, attracting 10,000 users during our measurement studies from February to July 2010, and providing over 1,000 cinematic-quality video streams with bit rates of 1 - 2 Mbps. Based on real-world traces collected over 6 months, we show that Novasky can achieve rapid startups within 4 - 9 seconds and extremely short seek latencies within 3 seconds, while maintaining reasonable operational overhead and server bandwidth costs. Our general understanding on the design tradeoffs of P2P storage cloud and practical experiences with Novasky may bring valuable guidelines to future designs of production-quality P2P storage cloud systems.

In this paper, we present Novasky, a real-world Video-on-Demand (VoD) system capable of delivering cinematic-quality video streams to end users. The foundation of the Novasky design is a peer-to-peer (P2P) storage cloud, storing and refreshing media streams in a decentralized fashion using local storage spaces of end users. We present our design objectives in Novasky, and how these objectives are achieved using a collection of unique mechanisms, with respect to caching strategies, coding mechanisms, and the maintenance of the supply-demand relationship when it comes to media availability in the P2P storage cloud. The production Novasky system has been implemented with over 100,000 lines of code. It has been deployed in the Tsinghua University campus network, operational since September 2009, attracting 10,000 users to date, and providing over 1,000 cinematic-quality video streams with bit rates of 1 - 2 Mbps. Based on real-world traces collected over 6 months, we show that Novasky can achieve rapid startups within 4 - 9 seconds, and extremely short seek latencies within 3 seconds. Our empirical experiences with Novasky may bring valuable insights to future designs of production-quality P2P storage cloud systems.