Allmydata, Inc. [1], provider of the "Allmydata" consumer backup product, is
pleased announce the first public release of "Tahoe", an open source
decentralized storage mesh.

The source code that we are releasing is the current working prototype for
Allmydata's next-generation product.  This prototype is not recommended for
storage of confidential data nor for data which is not otherwise backed up,
but it is already implements a functional decentralized storage mesh and is
useful for experimentation, prototyping, and extension.


Installation

This release of Tahoe is guaranteed to work only on Linux.  It may actually
work on other platforms -- earlier development revisions have been used on
Windows, Cygwin, Mac/Intel, and Mac/PPC -- but not all of the unit tests
currently pass on all platforms (see "Hacking and Community", below), so
we're officially proclaiming that it works on Linux.

To install, download the "Tahoe" tarball from the web server [2], untar it,
cd into the resulting directory, and follow the directions in the README [3].


Usage

XYZ Brian: please insert intro to UI


Hacking and Community

Please join our mailing list [4] and to discuss the ideas behind Tahoe and
extensions of and uses of Tahoe.  Patches that extend and improve Tahoe are
gratefully accepted -- roadmap.txt [5] shows the next improvements that we
plan to make.  You can browse the revision control history, source code, and
issue tracking at our Trac instance [6].  Please note the buildbot results
page [7], which show how Tahoe builds and passes unit tests on each checkin,
and the code coverage results [8] and percentage-covered graph [9], which
show how much of the Tahoe source code is currently exercised the test suite.


Licence

Tahoe is offered under the GNU General Public License (v2).  It also comes
with the added permission that, in the case that you are obligated to release
a derived work under this licence (as per section 2.b of the GPLv2), you may
delay the fulfillment of this obligation for up to 12 months.


Network Architecture

Each peer maintains a connection to each other peer.  A single distinct
server called an "introducer" is used to discover other peers with which to
connect.

To store a file, the file is encrypted and erasure coded, and each resulting
share is uploaded to a different peer.  The secure hash of the encrypted file
and the encryption key are packed into a URI, knowledge of which is necessary
and sufficient to recover the file.

To fetch a file, starting with the URI, a subset of shares is downloaded from
peers, the file is reconstructed from the shares, and then decrypted.

A single distinct server called a "vdrive server" maintains a mapping from
pathnames/filenames to URIs.

We are well aware of the limitations of decentralization and scalability
inherent in this prototype.  In particular, the completely-connected property
of the mesh and the requirement of a single distinct introducer and vdrive
server limits the possible size of the mesh.  We have plans to loosen these
limitations (see roadmap.txt [5]).  Currently it should be noted that the
mesh already depends as little as possible on the accessibility and
correctness of the introduction server and the vdrive server, and the choice
of which servers to use is easily configured.


Software Architecture

Tahoe is a "from the ground-up" rewrite, inspired by Allmydata's existing
consumer backup service, written in Python.

It uses the Foolscap library [10] which provides a remote object protocol
inspired by the capability-secure "E" programming language [11].  Foolscap
allows us to express the intended behavior of our distributed mesh directly
in object-oriented terms while relying on a well-engineered, secure transport
layer.

The underlying networking is provided by the Twisted library [12].
Computationally intensive operations are performed in native compiled code,
such as the "zfec" library for fast erasure coding (also available
separately: [13]).


[1]  http://allmydata.com
[2]  http://allmydata.com/source/tahoe-0.1.0-0-UNSTABLE.tar.bz2
[3]  http://allmydata.com/source/tahoe/README
[4]  https://postman.allmydata.com/cgi-bin/mailman/listinfo/tahoe XYZ Zandr or someone: right URL?
[5]  http://allmydata.com/source/tahoe/roadmap.txt
[6]  http://allmydata.org/trac XYZ Brian: right URL?
[7]  http://allmydata.org/buildbot XYZ Brian: right URL?
[8]  http://allmydata.org/code coverage thingie XYZ Brian: right URL?
[9]  http://allmydata.org/munin XYZ Brian: right URL?
[10] http://twistedmatrix.com/trac/wiki/FoolsCap
[11] http://erights.org/
[12] http://twistedmatrix.com/
[13] http://allmydata.com/source/zfec