Hadoop Datanode节点无法启动（All directories in dfs.data.dir are invalid）

java.io.IOException: All directories in dfs.datanode.data.dir are invalid: "/usr/local/hadoop-2.4.0/dfs/data" 
    at org.apache.hadoop.hdfs.server.datanode.DataNode.checkStorageLocations(DataNode.java:1900)
    at org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(DataNode.java:1873)
    at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1772)
    at org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:1812)
    at org.apache.hadoop.hdfs.server.datanode.DataNode.secureMain(DataNode.java:1988)
    at org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:2012)
2014-08-26 20:02:08,720 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 1

root@VM_160_34_centos:/usr/local/hadoop-2.4.0> chmod -R 755 dfs