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https://issues.apache.org/jira/browse/HDFS-3570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14636317#comment-14636317
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Akira AJISAKA commented on HDFS-3570:
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Thanks [~anu] for the comment.
bq. I see we are still referring to capacity in the old sense.
Agree.
bq. Would that mean now we have two different views of what is the available
capacity of a DN; That is, one that is viewed from the balancer vs. something
like {{DFSClient.getDatanodeReport}}.
Balancer uses {{DFSClient.getDatanodeStorageReport}}, so these views look the
same to me. We need to take into account non-DFS usage.
> 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 & mover
> Affects Versions: 2.0.0-alpha
> Reporter: Harsh J
> Assignee: Akira AJISAKA
> Priority: Minor
> Attachments: HDFS-3570.2.patch, 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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