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Date: Mon, 20 Oct 2008 11:19:46 -0700 (PDT)
From: "Raghu Angadi (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (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:comment-tabpanel&focusedCommentId=12641094#action_12641094 ] 

Raghu Angadi commented on HADOOP-4430:
--------------------------------------

What is the worst case possible if some one upgrades without noting the changes?

> 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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