共计 3938 个字符，预计需要花费 10 分钟才能阅读完成。
今早一来，突然发现使用 -put 命令往 HDFS 里传数据传不上去了，抱一大堆错误，然后我使用 bin/Hadoop dfsadmin -report 查看系统状态
admin@adw1:/home/admin/joe.wangh/hadoop-0.19.2>bin/hadoop dfsadmin -report
Configured Capacity: 0 (0 KB)
Present Capacity: 0 (0 KB)
DFS Remaining: 0 (0 KB)
DFS Used: 0 (0 KB)
DFS Used%: ?%
————————————————-
Datanodes available: 0 (0 total, 0 dead)
使用 bin/stop-all.sh 关闭 HADOOP
admin@adw1:/home/admin/joe.wangh/hadoop-0.19.2>bin/stop-all.sh
stopping jobtracker
172.16.197.192: stopping tasktracker
172.16.197.193: stopping tasktracker
stopping namenode
172.16.197.193: no datanode to stop
172.16.197.192: no datanode to stop
172.16.197.191: stopping secondarynamenode
哦，看到了吧，发现 datanode 前面并没有启动起来。去 DATANODE 上查看一下日志
admin@adw2:/home/admin/joe.wangh/hadoop-0.19.2/logs>vi hadoop-admin-datanode-adw2.hst.ali.dw.alidc.net.log
************************************************************/
2010-07-21 10:12:11,987 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException: Incompatible namespaceIDs in /home/admin/joe.wangh/hadoop/data/dfs.data.dir: namenode namespaceID = 898136669; datanode namespaceID = 2127444065
at org.apache.hadoop.hdfs.server.datanode.DataStorage.doTransition(DataStorage.java:233)
at org.apache.hadoop.hdfs.server.datanode.DataStorage.recoverTransitionRead(DataStorage.java:148)
at org.apache.hadoop.hdfs.server.datanode.DataNode.startDataNode(DataNode.java:288)
at org.apache.hadoop.hdfs.server.datanode.DataNode.<init>(DataNode.java:206)
at org.apache.hadoop.hdfs.server.datanode.DataNode.makeInstance(DataNode.java:1239)
at org.apache.hadoop.hdfs.server.datanode.DataNode.instantiateDataNode(DataNode.java:1194)
at org.apache.hadoop.hdfs.server.datanode.DataNode.createDataNode(DataNode.java:1202)
at org.apache.hadoop.hdfs.server.datanode.DataNode.main(DataNode.java:1324)
……
错误提示 namespaceIDs 不一致。
下面给出两种解决办法，我使用的是第二种。
Workaround 1: Start from scratch
I can testify that the following steps solve this error, but the side effects won’t 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 dfs.data.dir 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.
Workaround 2: 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 <dfs.data.dir>/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: dfs.data.dir 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 <dfs.data.dir>/current/VERSION
namespaceID=393514426
storageID=DS-1706792599-10.10.10.1-50010-1204306713481
cTime=1215607609074
storageType=DATA_NODE
layoutVersion=-13
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.
相关阅读 ：
Ubuntu 13.04 上搭建 Hadoop 环境 http://www.linuxidc.com/Linux/2013-06/86106.htm
Ubuntu 12.10 +Hadoop 1.2.1 版本集群配置 http://www.linuxidc.com/Linux/2013-09/90600.htm
Ubuntu 上搭建 Hadoop 环境（单机模式 + 伪分布模式）http://www.linuxidc.com/Linux/2013-01/77681.htm
Ubuntu 下 Hadoop 环境的配置 http://www.linuxidc.com/Linux/2012-11/74539.htm
单机版搭建 Hadoop 环境图文教程详解 http://www.linuxidc.com/Linux/2012-02/53927.htm
搭建 Hadoop 环境（在 Winodws 环境下用虚拟机虚拟两个 Ubuntu 系统进行搭建）http://www.linuxidc.com/Linux/2011-12/48894.htm
更多 Hadoop 相关信息见 Hadoop 专题页面 http://www.linuxidc.com/topicnews.aspx?tid=13
