tahoe-lafs/docs/proposed

The lossmodel.lyx file is the source document for an in-progress paper
that analyzes the probability of losing files stored in a Tahoe-LAFS
file store under various scenarios.  It describes:

1.  How to estimate peer reliabilities, based on peer MTBF failure
data.

2.  How to compute file loss probabilities, based on a given set of
shares stored on peers with estimated reliabilities.  The peer
reliabilities do not have to be uniform, and the model takes into
account the file repair process.

3.  How to estimate Tahoe parameters for k (shares needed), n (shares
distributed) and A (repair interval) to achieve a file reliability
target.

4.  How to compute the estimated repair cost over time, discounted at
a fixed rate, of maintaining a file for a time period T.

Future work will also address the latter three issues in the context
of "non-aggressive" repair, where repair will only be performed if
too many shares are lost, and it will also extend the repair cost
estimation model to suggest cost functions appropriate for common
network architectures.

A PDF of the current version of the file may be downloaded from:

    http://willden.org/~shawn/lossmodel.pdf