Scenario is a cluster spanning across datacenters and we use Local_quorum and want to know when things are not getting replicated across data centers. What is the best way to track/alert on that? 

I was planning on using the HintedHandOffManager (JMX) => org.apache.cassandra.db:type=HintedHandoffManager countPendingHints. Are there other metrics (maybe exposed via nodetool) I should be looking at. At this point we are on 1.1.6 cassandra.