@Override
  public ValidationLevel getValidationLevel() {
    return ValidationLevel.SERVER_HOST_RACK;
  }
If enabled, this class will help the balancer ensure that replicas aren't placed on the same
servers or racks as their primary. Configure this via
{@link BalancerConditionals#DISTRIBUTE_REPLICAS_KEY}
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/DistributeReplicasConditional.java