Ceph

This is a hypothetical but plausible problem.

If a group of monitors and OSDs are partitioned out, they will be detected and fenced out.
But consider ...
two large sites (A and B) interconnected by a fat pipe.
a third site (C) interconnected with A & B by thin pipes for quorum.
the fat pipe is severed (which does not sound too pathological).

the monitors would probably consider all of the OSDs to be up and in,
even though many cannot talk to one another. This seems to be a situation
in which we would behave very badly. Detecting arbitrary partitionings is
probably hard, but topologically obvious partitions might be detectable ...
after which we could choose a winner and a loser and get on with life.