In systems distributed on unreliable networks,
state must be available from more than one location
to avoid state loss in case of lost hosts or network
partitioning.
Classic argument between large invulnerable server
and several less reliable but redundant smaller servers.
Any one portion of the state should be available
from several peers.
When one peer disappears, another must be nominated
and provided with a copy of the state.
Peers holding duplicate copies of the state should
be selected to avoid a single common point of
failure -- the backhoe problem.