无法正常启动DataNode

2017-01-16 22:43:19,028 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: chan.takchi/192.168.42.129:9000. Already tried 9 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1000 MILLISECONDS)
2017-01-16 22:43:19,030 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Problem connecting to server: chan.takchi/192.168.42.129:9000
2017-01-16 22:43:24,364 INFO org.apache.hadoop.hdfs.server.common.Storage: Using 1 threads to upgrade data directories (dfs.datanode.parallel.volumes.load.threads.num=1, dataDirs=1)
2017-01-16 22:43:24,374 INFO org.apache.hadoop.hdfs.server.common.Storage: Lock on /usr/local/hdfs/data/in_use.lock acquired by nodename 18264@ubuntu
2017-01-16 22:43:24,376 WARN org.apache.hadoop.hdfs.server.common.Storage: Failed to add storage directory [DISK]file:/usr/local/hdfs/data/
java.io.IOException: Incompatible clusterIDs in /usr/local/hdfs/data: namenode clusterID = CID-f3f28bb6-58da-4ec9-bcef-eca58a6f912c; datanode clusterID = CID-6e31589b-654c-4772-a276-729db72ad48c
 at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:775)
 at org.apache.hadoop.hdfs.server.datanode.DataStorage.loadStorageDirectory(DataStorage.java:300)
 at org.apache.hadoop.hdfs.server.datanode.DataStorage.loadDataStorage(DataStorage.java:416)
 at org.apache.hadoop.hdfs.server.datanode.DataStorage.addStorageLocations(DataStorage.java:395)
 at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:573)
 at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1362)
 at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1327)
 at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:317)
 at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:223)
 at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:802)

原因在于我重新格式化了NameNode，而没有删掉DataNode相应的数据，导致DataNode与NameNode版本号不一致的错误。解决办法：停止fds服务，把NameNode以及DataNode对应文件夹里的数据删除后，重新格式化NameNode即可。