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From "Akira AJISAKA (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3570) Balancer shouldn't rely on "DFS Space Used %" as that ignores non-DFS used space
Date Thu, 06 Feb 2014 05:34:09 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13893062#comment-13893062

Akira AJISAKA commented on HDFS-3570:

I'll add a test. Thanks, [~ash211]!

> Balancer shouldn't rely on "DFS Space Used %" as that ignores non-DFS used space
> --------------------------------------------------------------------------------
>                 Key: HDFS-3570
>                 URL: https://issues.apache.org/jira/browse/HDFS-3570
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: balancer
>    Affects Versions: 2.0.0-alpha
>            Reporter: Harsh J
>            Priority: Minor
>         Attachments: HDFS-3570.aash.1.patch
> Report from a user here: https://groups.google.com/a/cloudera.org/d/msg/cdh-user/pIhNyDVxdVY/b7ENZmEvBjIJ,
post archived at http://pastebin.com/eVFkk0A0
> This user had a specific DN that had a large non-DFS usage among dfs.data.dirs, and very
little DFS usage (which is computed against total possible capacity). 
> Balancer apparently only looks at the usage, and ignores to consider that non-DFS usage
may also be high on a DN/cluster. Hence, it thinks that if a DFS Usage report from DN is 8%
only, its got a lot of free space to write more blocks, when that isn't true as shown by the
case of this user. It went on scheduling writes to the DN to balance it out, but the DN simply
can't accept any more blocks as a result of its disks' state.
> I think it would be better if we _computed_ the actual utilization based on {{(100-(actual
remaining space))/(capacity)}}, as opposed to the current {{(dfs used)/(capacity)}}. Thoughts?
> This isn't very critical, however, cause it is very rare to see DN space being used for
non DN data, but it does expose a valid bug.

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