“Incompatible clusterIDs”的错误原因是在执行“hdfs namenode -format”之前，没有清空DataNode节点的data目录。
网上一些文章和帖子说是tmp目录，它本身也是没问题的，但Hadoop 2.4.0是data目录，实际上这个信息已经由日志的“/data/hadoop/hadoop-2.4.0/data”指出，所以不能死死的参照网上的解决办法，遇到问题时多仔细观察。
从上述描述不难看出，解决办法就是清空所有DataNode的data目录，但注意不要将data目录本身给删除了。
data目录由core-site.xml文件中的属性“dfs.datanode.data.dir”指定。
2014-04-17 19:30:33,075 INFO org.apache.hadoop.hdfs.server.common.Storage: Lock on /data/hadoop/hadoop-2.4.0/data/in_use.lock acquired by nodename 28326@localhost
2014-04-17 19:30:33,078 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for block pool Block pool <registering> (Datanode Uuid unassigned) service to /172.25.40.171:9001
java.io.IOException: Incompatible clusterIDs in /data/hadoop/hadoop-2.4.0/data: namenode clusterID = CID-50401d89-a33e-47bf-9d14-914d8f1c4862; datanode clusterID = CID-153d6fcb-d037-4156-b63a-10d6be224091
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:472)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:225)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:249)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:929)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:900)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:274)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:220)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:815)
at java.lang.Thread.run(Thread.java:744)
2014-04-17 19:30:33,081 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Ending block pool service for: Block pool <registering> (Datanode Uuid unassigned) service to /172.25.40.171:9001
2014-04-17 19:30:33,184 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Block pool ID needed, but service not yet registered with NN
java.lang.Exception: trace
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.getBlockPoolId(BPOfferService.java:143)
at org.apache.hadoop.hdfs.server.datanode.BlockPoolManager.remove(BlockPoolManager.java:91)
at org.apache.hadoop.hdfs.server.datanode.DataNode.shutdownBlockPool(DataNode.java:859)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.shutdownActor(BPOfferService.java:350)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.cleanUp(BPServiceActor.java:619)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:837)
at java.lang.Thread.run(Thread.java:744)
2014-04-17 19:30:33,184 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Removed Block pool <registering> (Datanode Uuid unassigned)
2014-04-17 19:30:33,184 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Block pool ID needed, but service not yet registered with NN
java.lang.Exception: trace
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.getBlockPoolId(BPOfferService.java:143)
at org.apache.hadoop.hdfs.server.datanode.DataNode.shutdownBlockPool(DataNode.java:861)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.shutdownActor(BPOfferService.java:350)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.cleanUp(BPServiceActor.java:619)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:837)
at java.lang.Thread.run(Thread.java:744)
2014-04-17 19:30:35,185 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Exiting Datanode
2014-04-17 19:30:35,187 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 0
2014-04-17 19:30:35,189 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: SHUTDOWN_MSG:
/************************************************************
SHUTDOWN_MSG: Shutting down DataNode at localhost/127.0.0.1
************************************************************/