Do not use small blocks for balancing the cluster
https://issues.apache.org/jira/browse/HDFS-8824
Allow Balancer to run faster
https://issues.apache.org/jira/browse/HDFS-8818
平衡设置的文章：https://community.hortonworks.com/articles/43849/hdfs-balancer-2-configurations-cli-options.html
线程不够会导致平衡卡死，评论说这样改参数可以绕过
By setting dfs.balancer.moverThreads to a value big than dfs.datanode.balance.max.concurrent.moves *