title: datanode failed with org.apache.hadoop.util.DiskChecker$DiskErrorException
body: <p>Recently, I installed Hadoop and formatted namenode . the namenode started well but  the  datanodes  started failed . here is  the datanode error log</p>
  
  <pre><code>  STARTUP_MSG:   build = git@github.com:hortonworks/hadoop.git -r 3091053c59a62c82d82c9f778c48bde5ef0a89a1; compiled by 'jenkins' on 2018-05-11T07:53Z
  STARTUP_MSG:   java = 1.8.0_181
  ************************************************************/
  2018-10-17 15:08:42,769 INFO  datanode.DataNode (LogAdapter.java:info(47)) - registered UNIX signal handlers for [TERM, HUP, INT]
  2018-10-17 15:08:43,665 INFO  checker.ThrottledAsyncChecker (ThrottledAsyncChecker.java:schedule(122)) - Scheduling a check for [DISK]file:/hadoop/hdfs/data/
  2018-10-17 15:08:43,682 ERROR datanode.DataNode (DataNode.java:secureMain(2692)) - Exception in secureMain
  org.apache.hadoop.util.DiskChecker$DiskErrorException: Invalid value configured for dfs.datanode.failed.volumes.tolerated - 1. Value configured is &gt;= to the number of configured volumes (1).
      at org.apache.hadoop.hdfs.server.datanode.checker.StorageLocationChecker.check(StorageLocationChecker.java:174)
      at org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(DataNode.java:2584)
      at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:2493)
      at org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:2540)
      at org.apache.hadoop.hdfs.server.datanode.DataNode.secureMain(DataNode.java:2685)
      at org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:2709)
  2018-10-17 15:08:43,688 INFO  util.ExitUtil (ExitUtil.java:terminate(124)) - Exiting with status 1
  2018-10-17 15:08:43,696 INFO  datanode.DataNode (LogAdapter.java:info(47)) - SHUTDOWN_MSG: 
  /************************************************************
  SHUTDOWN_MSG: Shutting down DataNode at hdp2.com/192.168.100.12
  </code></pre>
  
  <p>what  does  <code>dfs.datanode.failed.volumes.tolerated - 1</code>   means ?   What caused such a mistake?</p>