五 02 十一月 2012




2012-07-21 10:12:11,987 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: Incompatible namespaceIDs in /home/admin/joe.wangh/hadoop/data/ namenode namespaceID = 898136669; datanode namespaceID = 2127444065
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.(
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.main(




Start from scratch
I can testify that the following steps solve this error, but the side effects wont make you happy (me neither). The crude workaround I have found is to:
1. stop the cluster
2. delete the data directory on the problematic datanode: the directory is specified by in conf/hdfs-site.xml; if you followed this tutorial, the relevant directory is /usr/local/hadoop-datastore/hadoop-hadoop/dfs/data
3. reformat the namenode (NOTE: all HDFS data is lost during this process!)
4. restart the cluster
When deleting all the HDFS data and starting from scratch does not sound like a good idea (it might be ok during the initial setup/testing), you might give the second approach a try.


Updating namespaceID of problematic datanodes
Big thanks to Jared Stehler for the following suggestion. I have not tested it myself yet, but feel free to try it out and send me your feedback. This workaround is “minimally invasive” as you only have to edit one file on the problematic datanodes:
1. stop the datanode
2. edit the value of namespaceID in /current/VERSION to match the value of the current namenode
3. restart the datanode
If you followed the instructions in my tutorials, the full path of the relevant file is /usr/local/hadoop-datastore/hadoop-hadoop/dfs/data/current/VERSION (background: is by default set to ${hadoop.tmp.dir}/dfs/data, and we set hadoop.tmp.dir to /usr/local/hadoop-datastore/hadoop-hadoop).
If you wonder how the contents of VERSION look like, here’s one of mine:
#contents of /current/VERSION

原因:每次namenode format会重新创建一个namenodeId,而tmp/dfs/data下包含了上次format下的id,namenode format清空了namenode下的数据,但是没有晴空datanode下的数据,导致启动时失败,所要做的就是每次fotmat前,清空tmp一下 的所有目录.

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