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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "FAQ" by QwertyManiac
Date Thu, 10 Feb 2011 17:55:38 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.

The "FAQ" page has been changed by QwertyManiac.
http://wiki.apache.org/hadoop/FAQ?action=diff&rev1=90&rev2=91

--------------------------------------------------

  Learn more about safe mode [[http://hadoop.apache.org/hdfs/docs/current/hdfs_user_guide.html#Safemode|in
the HDFS Users' Guide]].
  
  == How do I set up a hadoop node to use multiple volumes? ==
- ''Data-nodes'' can store blocks in multiple directories typically allocated on different
local disk drives. In order to setup multiple directories one needs to specify a comma separated
list of pathnames as a value of the configuration parameter  [[http://hadoop.apache.org/core/docs/current/hadoop-default.html#dfs.data.dir|dfs.data.dir]].
Data-nodes will attempt to place equal amount of data in each of the directories.
+ ''Data-nodes'' can store blocks in multiple directories typically allocated on different
local disk drives. In order to setup multiple directories one needs to specify a comma separated
list of pathnames as a value of the configuration parameter  [[http://hadoop.apache.org/hdfs/docs/current/hdfs-default.html#dfs.datanode.data.dir|dfs.datanode.data.dir]].
Data-nodes will attempt to place equal amount of data in each of the directories.
  
- The ''name-node'' also supports multiple directories, which in the case store the name space
image and the edits log. The directories are specified via the  [[http://hadoop.apache.org/core/docs/current/hadoop-default.html#dfs.name.dir|dfs.name.dir]]
configuration parameter. The name-node directories are used for the name space data replication
so that the image and the  log could be restored from the remaining volumes if one of them
fails.
+ The ''name-node'' also supports multiple directories, which in the case store the name space
image and the edits log. The directories are specified via the  [[http://hadoop.apache.org/hdfs/docs/current/hdfs-default.html#dfs.namenode.name.dir|dfs.namenode.name.dir]]
configuration parameter. The name-node directories are used for the name space data replication
so that the image and the  log could be restored from the remaining volumes if one of them
fails.
  
  == What happens if one Hadoop client renames a file or a directory containing this file
while another client is still writing into it? ==
  Starting with release hadoop-0.15, a file will appear in the name space as soon as it is
created.  If a writer is writing to a file and another client renames either the file itself
or any of its path  components, then the original writer will get an IOException either when
it finishes writing to the current  block or when it closes the file.

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