For incompatible namespaceid error, there are two solutions available here.


I ran into this same issue and second solution fixed it.



From: anil gupta []
Sent: Wednesday, August 08, 2012 1:36 PM
Subject: Re: Data node error


This link might provide you some more information:


On Wed, Aug 8, 2012 at 12:56 AM, anil gupta <> wrote:

Hi Prabhu,

Did you clean the data dir on DataNodes? Whenever Namenode is formated the data directories of Datanodes needs to be cleaned up. As far as i remember it's the directory which you mention in in hdfs-site.xml file.You can do a google search for the error and you can get more details.
(Sorry, i dont have access to my cluster conf right now for telling you the exact property).



On Wed, Aug 8, 2012 at 12:49 AM, prabhu K <> wrote:

Hi Users,


I have formatted hadoop cluster, formatted successfully. after stop &start hadoop, i hit the jps command in master, getting fine, but in slave machine am not getting data node, while see the data node log file, i am getting following error.


Data node(slave1):

2012-08-08 00:16:44,033 WARN org.apache.hadoop.hdfs.server.datanode.DataBlockScanner: Second Verification failed for blk_-3831635302961953167_1690. Exception :
IOException: Block blk_-3831635302961953167_1690 is not valid.
        at org.apache.hadoop.hdfs.server.datanode.FSDataset.getBlockFile(
        at org.apache.hadoop.hdfs.server.datanode.FSDataset.getLength(
        at org.apache.hadoop.hdfs.server.datanode.FSDataset.getVisibleLength(
        at org.apache.hadoop.hdfs.server.datanode.BlockSender.<init>(
        at org.apache.hadoop.hdfs.server.datanode.BlockSender.<init>(
        at org.apache.hadoop.hdfs.server.datanode.DataBlockScanner.verifyBlock(
        at org.apache.hadoop.hdfs.server.datanode.DataBlockScanner.verifyFirstBlock(

data node(slave2)

2012-08-08 13:03:50,195 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Incompatible namespaceIDs in /app/hadoop/tmp/dfs/data: namenode name
spaceID = 1434906924; datanode namespaceID = 474761520
        at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(
        at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(
        at org.apache.hadoop.hdfs.server.datanode.DataNode.startDataNode(
        at org.apache.hadoop.hdfs.server.datanode.DataNode.<init>(
        at org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(
        at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(
        at org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(
        at org.apache.hadoop.hdfs.server.datanode.DataNode.secureMain(
        at org.apache.hadoop.hdfs.server.datanode.DataNode.main(


Please help me on this issue.




Thanks & Regards,
Anil Gupta

Thanks & Regards,
Anil Gupta