This cluster parameter consists of a "hasTwoOrMoreShards" boolean which must be set and unset atomically with add/remove shard operation. It should reflect the real cardinality of the cluster so shouldn't be settable by external users (unless we think that admin users might need to set it manually if this parameter somehow has incorrect value due to a bug). Currently, this cluster parameter is not documented, so no users should know about it and try to set it. But if we decide to do this ticket, a uassert to prevent this cluster parameter might be needed since currently there isn't a way to specify a cluster parameter as internal-only,