Guarantees From

33 CHAOS T he P2P revolution promises freedom from boundaries, censorship, and centralized control. P2P proponents claim the vast untapped resource of personal computers owned by ordinary people can be combined together to build something greater and more reliable than the sum of its parts. Each participating computer or node in a P2P system is called a " peer, " meaning that participants interact as equals. Peers play a variety of roles. When accessing information, they are clients. When serving information to other clients, they are servers. When forwarding information for others, they are routers. According to the P2P vision, thousands, millions, or even billions of peers may interact in a seething, transient pattern of communication. Architects of these systems claim this chaos can lead to properties such as " durability, " " anonymity, " " scalability, " and " security " —the list goes on. Can we really achieve guarantees in the chaotic P2P environment? The attainment of guarantees is a central concern of the OceanStore [7] project at Berkeley. As the chief architect of OceanStore, I present some principles that can be used to achieve guarantees in P2P systems. Although I use distributed file service to frame my ideas, the concepts are generally applicable. Distributed File Service Distributed file service is a " typical " P2P application. The idea is straightforward: replace the local hard disk of a computer with pools of storage spread throughout the Internet; the computer interacts with a vast web of peers to read or write information. Figure 1 illustrates this idea. Examples include FreeNet [6], Gnutella [6], FreeHaven [6], Publius [6], Intermemory [1], and OceanStore [7], to name a few. Let us start by highlighting some properties we might want to guarantee for our distributed file service: Extracting Architects of P2P systems claim thousands, millions, even billions will interact in a seething, transient pattern of communication. Can we really achieve guarantees in the chaotic P2P environment?