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Date: Tue, 21 Oct 2008 16:40:44 -0700 (PDT)
From: "Robert Chansler (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Updated: (HADOOP-4430) Namenode Web UI capacity report is
 inconsistent with Balancer
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     [ https://issues.apache.org/jira/browse/HADOOP-4430?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Robert Chansler updated HADOOP-4430:
------------------------------------

    Release Note: 
Changed reporting in the NameNode Web UI to more closely reflect the behavior of the re-balancer. Removed no longer used config parameter dfs.datanode.du.pct from hadoop-default.xml.


  was:
Incompatible changes:
This change modifies/retains the changes made in 2816 as follows:
1) Present Capacity added in 2816 is removed from the Web UI
2) Change of Total Capacity to Configured Capacity and its definition from 2816 is retained in the Web UI
3) Data node protocol change to report Configured Capacity instead of Total Capacity is retained.
4) DFS Used% was calculated as a percentage of Present Capacity. It is changed to percentage of Configured Capacity.

Other incompatible changes:
1) Config parameter dfs.datanode.du.pct is no longer used and is removed from the hadoop-default.xml.

2) Namenode Web UI has the following addional changes:
   The following parameters are added to both Cluster Summary and Datanode information:
   * Non DFS Used - This indicates the disk space taken by non DFS file
   * DFS remaining % - This is remaining % of Configured Capacity available for DFS use


    Hadoop Flags: [Incompatible change, Reviewed]  (was: [Reviewed, Incompatible change])

> Namenode Web UI capacity report is inconsistent with Balancer
> -------------------------------------------------------------
>
>                 Key: HADOOP-4430
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4430
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.19.0
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>            Priority: Blocker
>             Fix For: 0.19.0
>
>         Attachments: HADOOP-4430.patch, HADOOP-4430.patch, HADOOP-4430.patch
>
>
> Solution to 2816 changed
> - Total Capacity definition from (the disk space of all data directories) to (the disk space of all the data directories - the reserved space)
> - We added a new element Present Capacity to the report. It is set to (Used Capacity + Remaining Capacity)
> - We changed the Used Percentage reported from (Used Capacity)/(Total Capacity) to (Used Capacity)/(Present Capacity)
> - All these changes are displayed on Namenode Web UI.
> Balancer functionality
> Balancer script is started with a threshold parameter. It tries to move the blocks from the nodes that have Used % that is more than (Cluster average + threshold) to the nodes that have less than (Cluster average - threshold). Essentially balancer gets all the datanodes used % to with in (the Cluster average +/- threshold).
> Inconsistencies due to the change in 2816
> When MapReduce jobs are run, temporary files are generated. This eats away a lot of space from Present Capacity. The difference between the Total Capacity and the Present Capacity can be huge. Currently balancer computes Used Percentage based (Used Capacity)/(Total Capacity). The Used % the balancer uses could be significantly different from Used % displayed on the Namenode Web UI. When balancer is done balancing, the Namenode Used % might still appear unbalanced.

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