A Cooperative File System

The Cooperative File System (CFS) is a new peer-to-peer read-only storage system that provides provable guarantees for the efficiency, robustness, and load-balance of file storage and retrieval. CFS does this with a completely decentralized architecture that can scale to large systems. CFS servers provide a distributed hash table (DHash) for block storage. CFS clients interpret DHash blocks as a file system. DHash distributes and caches blocks at a fine granularity to achieve load balance, uses replication for robustness, and decreases latency with server selection. DHash finds blocks using the Chord location protocol, which operates in time logarithmic in the number of servers and requires logarithmic state at each node. CFS is implemented using the SFS file system toolkit and runs on many UNIX operating systems including Linux, OpenBSD, and FreeBSD. Experience on a globally deployed prototype shows that CFS delivers data to clients as fast as FTP. Controlled tests show that CFS is able to route queries in a scalable way. For example, in experiments with a system of 4,096 servers, looking up a block of data involves contacting only seven servers. In general, a logarithmic number of servers must be contacted to route a query. Servers are also able to join and leave the system efficiently. Tests demonstrate nearly perfect robustness and unimpaired performance even when as many as half the servers fail. Thesis Supervisor: M. Frans Kaashoek Title: Professor of Computer Science and Engineering Thesis Supervisor: Robert T. Morris Title: Assistant Professor of Computer Science and Engineering