||Though online storage systems in the Internet have provided valuable services to share files among end users, such services are typically provided by dedicated servers with prohibitive server bandwidth costs as the systems scale up. It is intuitive, but non-trivial, to mitigate such costs by taking advantage of peer upload bandwidth in a complementary fashion. This thesis presents FS2You, a large-scale and real-world online storage and distribution system with peer assistance and semi-persistent file availability. FS2You is designed to dramatically mitigate server bandwidth costs. In this thesis, we show a number of key challenges involved in such a design objective, our architectural and protocol design in response to these challenges, as well as an extensive measurement study at a large scale to demonstrate the effectiveness of our design, using real-world traces that we have collected. Furthermore, we propose a dedicated server protocol design model for such systems, in order to make better use of limited server storage and bandwidth resources to guarantee adequate levels of service quality in terms of file availability and downloading performance. Our design serves as a framework with tunable design knobs offering flexible design choices to service providers. Using real-world dataset that we have collected, we evaluate our protocol design through extensive experimental studies from different perspectives, which demonstrate the effectiveness of our design and a number of practical guidelines. To our knowledge, this study represents the first attempt to design, implement, evaluate and model a new peer-assisted semi-persistent online storage and distribution system at a realistic scale.