今天启动Hadoop2.2.0集群后，发现datanode进程没启动，查看日志发现如下报错：
2014-05-15 14:46:50,788 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Initialization failed for block pool Block pool BP-2020521428-192.168.0.166-1397704506565 (storage id DS-432251277-192.168.0.166-50010-1397704557407)
service to singlehadoop/192.168.0.166:8020
service to singlehadoop/192.168.0.166:8020
java.io.IOException: Incompatible clusterIDs in /home/casliyang/hadoop2/hadoop-2.2.0/metadata/data: namenode clusterID
= CID-2cc69ada-3730-4c79-8384-c725fa85859a; datanode clusterID
= CID-3e649eb6-cdb3-4a0c-aad8-5948c66bf282
= CID-2cc69ada-3730-4c79-8384-c725fa85859a; datanode clusterID
= CID-3e649eb6-cdb3-4a0c-aad8-5948c66bf282
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:391)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:191)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:219)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initStorage(DataNode.java:837)
at org.apache.hadoop.hdfs.server.datanode.DataNode.initBlockPool(DataNode.java:808)
at org.apache.hadoop.hdfs.server.datanode.BPOfferService.verifyAndSetNamespaceInfo(BPOfferService.java:280)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:222)
at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:664)
at java.lang.Thread.run(Thread.java:722)
上网查了下，有些文章说的解决办法是删掉数据文件，格式化，重启集群，但这办法实在太暴力，根本无法在生产环境实施，所以还是参考另一类文章的解决办法，修改clusterID：
step1：
查看hdfs-site.xml，找到存namenode元数据和datanode元数据的路径：
<property>
<name>dfs.namenode.name.dir</name>
<value>file:///home/casliyang/hadoop2/hadoop-2.2.0/metadata/name</value>
</property>
<property>
<name>dfs.datanode.data.dir</name>
<value>file:///home/casliyang/hadoop2/hadoop-2.2.0/metadata/data</value>
</property>
step2：
打开namenode路径下的current/VERSION文件：
casliyang@singlehadoop:~/hadoop2/hadoop-2.2.0/metadata/name/current$ cat VERSION
#Thu May 15 14:46:39 CST 2014
namespaceID=1252551786
clusterID=CID-2cc69ada-3730-4c79-8384-c725fa85859a
cTime=0
storageType=NAME_NODE
blockpoolID=BP-2020521428-192.168.0.166-1397704506565
layoutVersion=-47
打开datanode路径下的current/VERSION文件：
casliyang@singlehadoop:~/hadoop2/hadoop-2.2.0/metadata/data/current$ cat VERSION
#Thu Apr 17 11:15:57 CST 2014
storageID=DS-432251277-192.168.0.166-50010-1397704557407
clusterID=CID-3e649eb6-cdb3-4a0c-aad8-5948c66bf282
cTime=0
storageType=DATA_NODE
layoutVersion=-47
我们可以看到，name节点元数据的clusterID和data节点元数据的clusterID不一致了，并且和报错信息完全对应上！
接下来将data节点的clusterID修改成和name节点的clusterID一致，重启集群即可。
