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The Chord project explored how to build scalable, robust distributed systems using peer-to-peer ideas. The basis for much of our work is the Chord distributed hash lookup primitive. Chord is completely decentralized and symmetric, and can find data using only log(N) messages, where N is the number of nodes in the system. Chord's lookup mechanism is provably robust in the face of frequent node failures and re-joins.
On top of Chord's routing layer, we have built the DHash block storage system.
DHash provides a simple
get interface to store and retrieve
objects. Recent research has focused on developing algorithms to
efficiently maintain replicas
of these objects over long periods to provide
availability and durability.
Systems we have prototyped that use Chord and DHash include CFS (Cooperative File System), UsenetDHT, and OverCite. CFS allows anyone to publish and update their own file system, and provides read-only access to others; UsenetDHT allows Usenet servers to share storage instead of fully replicating articles locally; OverCite is a distributed version of the CiteSeer digital library. These systems all takes advantage of Chord and DHash to distribute the load of serving data very widely to achieve high performance despite flash crowds. DHash abstracts the process of replicating data and maintaining that replication as nodes fail and re-join the system.
At this point no official release for Chord is available. This source repository contains the complete development history.
This version is experimental, and no longer under active development, and is probably broken. The Chord HOWTO describes in more detail how to download and compile the software. The codebase is licensed under an MIT/X11-style license.
We gratefully acknowledge funding for Chord from DARPA and the Space and Naval Warfare Systems Center (SPAWAR), San Diego, under contract N66001-00-1-8933 which also funded the RON project. Chord was also supported by LCS's Project Oxygen and NTT. Some of our developers were funded by the Cambridge-MIT Institute. Most of our funding came from Project IRIS.
The Chord project uses the services of the Utah Network Testbed and the PlanetLab Testbed. Some research simulations were conducted on the Sun Grid Compute utility.
We welcome feedback, suggestions, patches, and so forth. Send them to chord AT pdos.csail.mit.edu; you can subscribe or read the archives on the web.