If you format namenode, you need to cleanup storage directories of DataNode as well if that is having some data already. DN also will have namespace ID saved and compared with NN namespaceID. if you format NN, then namespaceID will be changed and DN may have still older namespaceID. So, just cleaning the data in DN would be fine.
Regards, Uma ________________________________ From: hadoop hive [hadooph...@gmail.com] Sent: Friday, November 16, 2012 1:15 PM To: user@hadoop.apache.org Subject: Re: High Availability - second namenode (master2) issue: Incompatible namespaceIDs Seems like you havn't format your cluster (if its 1st time made). On Fri, Nov 16, 2012 at 9:58 AM, a...@hsk.hk<mailto:a...@hsk.hk> <a...@hsk.hk<mailto:a...@hsk.hk>> wrote: Hi, 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; datanode namespaceID = 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), 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? Thanks
