Hadoop NameSpaceID Error

Below given is usual error occurred in Hadoop environment.

Error in logger will be:

ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException: Incompatible namespaceIDs

Solution:

Stop all hadoop daemons and then

1. vi $PATH_TO_HADOOP_DATASTORE/dfs/name/current/VERSION
2. Copy the namespaceID value.
3. Now open a terminal on every machine having a datanode and do the following:
     vi $PATH_TO_HADOOP_DATASTORE/dfs/data/current/VERSION
4. Delete the entry corresponding to namespaceID and paste the value copied in Step 1.
Then save and exit.
Start hadoop daemons.