public static double getMaxSkew(double total, double numServers) {
    if (numServers == 0) {
      return 0;
    }
    double mean = total / numServers;
    return Math.sqrt((total - mean) * (total - mean) + (numServers - 1) * mean * mean);
  }
Return the max deviation of distribution Compute max as if all region servers had 0 and one had
the sum of all costs. This must be a zero sum cost for this to make sense.
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/DoubleArrayCost.java