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https://issues.apache.org/jira/browse/HDFS-12555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16201505#comment-16201505
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luoge123 commented on HDFS-12555:
---------------------------------
In current federation function, if the /user directory has been configured as
follows :
<property>
<name>fs.viewfs.mounttable.nsX.link./user</name>
<value>hdfs://nn1:8020/user</value>
</property>
then, we can't add the follow /user/hive configuration to core-site.xml any
more.
<property>
<name>fs.viewfs.mounttable.nsX.link./user/hive</name>
<value>hdfs://nn2:8020/user/hive</value>
</property>
My improvement is that the two configuration items all exist in core-site.xml
at same time.
After support this configuration, we need copy data from
hdfs://nn1:8020/user/hive to hdfs://nn2:8020/user/hive, fastcp or distcp tools
can help us. And then we can delete hdfs://nn1:8020/user/hive.
After we done this, the meta data in /user directory except /user/hive all
manager by nn1, and read and write requests are send to nn1. The meta data for
/user/hive manager by nn2, read and write requests for /user/hive are send to
nn2.
I'm not sure this explanation could answer your question or not, if you have
any questions, please fell free to contact me.
> HDFS federation should support configure secondary directory
> -------------------------------------------------------------
>
> Key: HDFS-12555
> URL: https://issues.apache.org/jira/browse/HDFS-12555
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: federation
> Environment: 2.6.0-cdh5.10.0
> Reporter: luoge123
> Fix For: 2.6.0
>
> Attachments: HDFS-12555.001.patch
>
>
> HDFS federation support multiple namenodes horizontally scales the file
> system namespace. As the amount of data grows, using a single group of
> namenodes to manage a single directory, namenode still achieves performance
> bottlenecks. In order to reduce the pressure of namenode, we can split out
> the secondary directory, and manager it by a new namenode. This is
> transparent for users.
> For example, nn1 only manager the /user directory, when nn1 achieve
> performance bottlenecks, we can split out /user/hive directory, and ues nn2
> to manager it.
> That means core-site.xml should support as follows configuration.
> <property>
> <name>fs.viewfs.mounttable.nsX.link./user</name>
> <value>hdfs://nn1:8020/user</value>
> </property>
> <property>
> <name>fs.viewfs.mounttable.nsX.link./user/hive</name>
> <value>hdfs://nn2:8020/user/hive</value>
> </property>
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