  In this paper, we consider the problem of quantifying systemic redundancy in
reliable systems having multiple controllers with overlapping functionality. In
particular, we consider a multi-channel system with multi-controller
configurations -- where controllers are required to respond optimally, in the
sense of best-response correspondence, a {\it reliable-by-design} requirement,
to non-faulty controllers so as to ensure or maintain some system properties.
Here we introduce a mathematical framework, based on the notion of relative
entropy of probability measures associated with steady-state solutions of
Fokker-Planck equations for a family of stochastically perturbed multi-channel
systems, that provides useful information towards a systemic assessment of
redundancy in the system.
