@Override
          public HDFSBlocksDistribution call() throws Exception {
            return internalGetTopBlockLocation(hri);
          }
This will find where data for a region is located in HDFS. It ranks {@link ServerName}'s by the
size of the store files they are holding for a given region.
hbase-balancer/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionHDFSBlockLocationFinder.java