TFS: A Transparent File System for Contributory Storage

Contributory applications allow users to donate unused resources on their personal computers to a shared pool. Applications such as SETI@home, Folding@home, and Freenet are now in wide use and provide a variety of services, including data processing and content distribution. However, while several research projects have proposed contributory applications that support peer-to-peer storage systems, their adoption has been comparatively limited. We believe that a key barrier to the adoption of contributory storage systems is that contributing a large quantity of local storage interferes with the principal user of the machine. To overcome this barrier, we introduce the Transparent File System (TFS). TFS provides background tasks with large amounts of unreliable storage—all of the currently available space—without impacting the performance of ordinary file access operations. We show that TFS allows a peer-to-peer contributory storage system to provide 40% more storage at twice the performance when compared to a user-space storage mechanism. We analyze the impact of TFS on replication in peer-to-peer storage systems and show that TFS does not appreciably increase the resources needed for file replication.