WARN hdfs.DFSClient: DataStreamer Exception: org.apache.hadoop.ipc.RemoteException: java.io.IOException: File /input/LICENSE.txt could only be replicated to 0 nodes, instead of 1
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:1920)
        at org.apache.hadoop.hdfs.server.namenode.NameNode.addBlock(NameNode.java:783)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:587)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1432)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1428)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1190)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1426)

        at org.apache.hadoop.ipc.Client.call(Client.java:1113)
        at org.apache.hadoop.ipc.RPC$Invoker.invoke(RPC.java:229)
        at $Proxy1.addBlock(Unknown Source)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:85)
        at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:62)
        at $Proxy1.addBlock(Unknown Source)
        at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.locateFollowingBlock(DFSClient.java:3720)
        at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.nextBlockOutputStream(DFSClient.java:3580)
        at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream.access$2600(DFSClient.java:2783)
        at org.apache.hadoop.hdfs.DFSClient$DFSOutputStream$DataStreamer.run(DFSClient.java:3023)

出现 这种异常是因为数据冲突造成的，可以把通过日志查看，解决办法：删掉tmp文件夹下生成的dfs文件，重新format一下，问题解决。

我的日志如下：通过日志进行删除：

2014-07-29 11:54:34,021 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: STARTUP_MSG: 
/************************************************************
STARTUP_MSG: Starting DataNode
STARTUP_MSG:   host = qa-lamp/10.110.30.30
STARTUP_MSG:   args = []
STARTUP_MSG:   version = 1.2.1
STARTUP_MSG:   build = https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.2 -r 1503152; compiled by ‘mattf‘ on Mon Jul 22 15:23:09 PDT 2013
STARTUP_MSG:   java = 1.6.0_32
************************************************************/
2014-07-29 11:54:34,197 INFO org.apache.hadoop.metrics2.impl.MetricsConfig: loaded properties from hadoop-metrics2.properties
2014-07-29 11:54:34,209 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source MetricsSystem,sub=Stats registered.
2014-07-29 11:54:34,210 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Scheduled snapshot period at 10 second(s).
2014-07-29 11:54:34,210 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: DataNode metrics system started
2014-07-29 11:54:34,315 INFO org.apache.hadoop.metrics2.impl.MetricsSourceAdapter: MBean for source ugi registered.
2014-07-29 11:54:34,716 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException: Incompatible namespaceIDs in /export/hadoop/tmp/dfs/data: namenode namespaceID = 1408593158; datanode namespaceID = 1322143693
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:232)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:147)
at org.apache.hadoop.hdfs.server.datanode.DataNode.startDataNode(DataNode.java:414)
at org.apache.hadoop.hdfs.server.datanode.DataNode.<init>(DataNode.java:321)
at org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(DataNode.java:1712)
at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1651)
at org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:1669)
at org.apache.hadoop.hdfs.server.datanode.DataNode.secureMain(DataNode.java:1795)
at org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:1812)