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From "Kartashov, Andy" <Andy.Kartas...@mpac.ca>
Subject RE: High Availability - second namenode (master2) issue: Incompatible namespaceIDs
Date Fri, 16 Nov 2012 14:11:10 GMT
Agreed here. Whenever you have id disagreement between NN and DN. Simply, delete all the entries
in your df/data directory and restart DN. No need to reformat NN.


From: shashwat shriparv [mailto:dwivedishashwat@gmail.com]
Sent: Friday, November 16, 2012 2:53 AM
To: user@hadoop.apache.org
Subject: Re: High Availability - second namenode (master2) issue: Incompatible namespaceIDs

Delete the VERSION for the datanode before format.

Shashwat Shriparv

On Fri, Nov 16, 2012 at 1:15 PM, hadoop hive <hadoophive@gmail.com<mailto:hadoophive@gmail.com>>
Seems like you havn't format your cluster (if its 1st time made).

On Fri, Nov 16, 2012 at 9:58 AM, ac@hsk.hk<mailto:ac@hsk.hk> <ac@hsk.hk<mailto:ac@hsk.hk>>

Please help!

I have installed a Hadoop Cluster with a single master (master1) and have HBase running on
the HDFS.  Now I am setting up the second master  (master2) in order to form HA.  When I used
JPS to check the cluster, I found :

2782 Jps
2126 NameNode
2720 SecondaryNameNode
i.e. The datanode on this server could not be started

In the log file, found:
2012-11-16 10:28:44,851 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException:
Incompatible namespaceIDs in /app/hadoop/tmp/dfs/data: namenode namespaceID = 1356148070<tel:1356148070>;
datanode namespaceID = 1151604993<tel:1151604993>

One of the possible solutions to fix this issue is to:  stop the cluster, reformat the NameNode,
restart the cluster.
QUESTION: As I already have HBASE running on the cluster, if I reformat the NameNode, do I
need to reinstall the entire HBASE? I don't mind to have all data lost as I don't have many
data in HBASE and HDFS, however I don't want to re-install HBASE again.

On the other hand, I have tried another solution: stop the DataNode, edit the namespaceID
in current/VERSION (i.e. set namespaceID=1151604993<tel:1151604993>), restart the datanode,
it doesn't work:
Warning: $HADOOP_HOME is deprecated.
starting master2, logging to /usr/local/hadoop-1.0.4/libexec/../logs/hadoop-hduser-master2-master2.out
Exception in thread "main" java.lang.NoClassDefFoundError: master2
Caused by: java.lang.ClassNotFoundException: master2
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Could not find the main class: master2.  Program will exit.
QUESTION: Any other solutions?


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