Package org.apache.hadoop.hdfs.server.diskbalancer.planner Description
Planner takes a DiskBalancerVolumeSet, threshold and
 computes a series of steps that lead to an even data
 distribution between volumes of this DiskBalancerVolumeSet.
 The main classes of this package are steps and planner.
 Here is a high level view of how planner operates:
 DiskBalancerVolumeSet current = volumeSet;
 while(current.isBalancingNeeded(thresholdValue)) {
   // Creates a plan , like move 20 GB data from v1 -> v2
   Step step = planner.plan(current, thresholdValue);
   // we add that to our plan
   planner.addStep(current, step);
   // Apply the step to current state of the diskSet to
   //compute the next state
   current = planner.apply(current, step);
 }
 //when we are done , return the list of steps
 return planner;