int getHostReplicaCount() {
    AmbryDataNode dataNode = instanceNameToAmbryDataNode.get(selfInstanceName);
    return ambryDataNodeToAmbryReplicas.get(dataNode).size();
  }
Callback method when this data node is becoming SEMI AUTO from FULL AUTO.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/HelixClusterManager.java