错误：datanode无法启动
查看日志如下:
2016-04-14 04:07:58,821 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool (Datanode Uuid unassigned) service to itcast01/192.168.1.201:9000. Exiting.
java.io.IOException: Incompatible clusterIDs in /itcast/hadoop-2.6.0/tmp/dfs/data: namenode clusterID = CID-fee4dcb4-9615-42c0-bd46-d3b4acf02e61; datanode clusterID = CID-9d6dfbcc-0f6f-47e3-9a79-d01cf5fc636b
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:646)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.addStorageLocations(DataStorage.java:320)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:403)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:422)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1311)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1276)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:314)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:220)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:828)
at java.lang.Thread.run(Thread.java:745)
2016-04-14 04:07:58,832 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool (Datanode Uuid unassigned) service to itcast01/192.168.1.201:9000
2016-04-14 04:07:58,838 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for Block pool (Datanode Uuid unassigned) service to itcast02/192.168.1.202:9000. Exiting.
java.io.IOException: Incompatible clusterIDs in /itcast/hadoop-2.6.0/tmp/dfs/data: namenode clusterID = CID-fee4dcb4-9615-42c0-bd46-d3b4acf02e61; datanode clusterID = CID-9d6dfbcc-0f6f-47e3-9a79-d01cf5fc636b
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:646)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.addStorageLocations(DataStorage.java:320)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:403)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:422)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:1311)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:1276)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:314)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:220)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:828)
at java.lang.Thread.run(Thread.java:745)
2016-04-14 04:07:58,839 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool (Datanode Uuid unassigned) service to itcast02/192.168.1.202:9000
2016-04-14 04:07:58,892 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Removed Block pool (Datanode Uuid unassigned)
2016-04-14 04:08:00,892 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Exiting Datanode
2016-04-14 04:08:00,923 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 0
2016-04-14 04:08:00,928 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: SHUTDOWN_MSG:
/*************************************************
SHUTDOWN_MSG: Shutting down DataNode at itcast05/192.168.1.205
**************************************************/
从日志上看，加粗的部分说明了问题
datanode的clusterID 和 namenode的clusterID 不匹配。
解决办法:
我的集群环境分布是这样的：
根据日志中的路径，在namenode节点上
cd /home/hadoop/tmp/dfs
在datanode节点上
cd /home/hadoop/tmp/dfs
能看到 data/current文件夹，
将data/current下的VERSION中的clusterID复制到data/current下的VERSION中，覆盖掉原来的clusterID
让两个clusterID保持一致
然后重启，启动后执行jps，查看datanode节点itcast05进程：
[root@itcast05 ~]# jps
3645 QuorumPeerMain
3715 JournalNode
4292 DataNode
5190 Jps
3976 NodeManager
