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https://issues.apache.org/jira/browse/HDFS-9837?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15160192#comment-15160192
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Rakesh R commented on HDFS-9837:
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Thanks [~jingzhao], +1 on the latest patch. Pending Jenkins.
> BlockManager#countNodes should be able to detect duplicated internal blocks
> ---------------------------------------------------------------------------
>
> Key: HDFS-9837
> URL: https://issues.apache.org/jira/browse/HDFS-9837
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Affects Versions: 3.0.0
> Reporter: Jing Zhao
> Assignee: Jing Zhao
> Attachments: HDFS-9837.000.patch, HDFS-9837.001.patch,
> HDFS-9837.002.patch, HDFS-9837.003.patch, HDFS-9837.004.patch
>
>
> Currently {{BlockManager#countNodes}} only counts the number of
> replicas/internal blocks thus it cannot detect the under-replicated scenario
> where a striped EC block has 9 internal blocks but contains duplicated
> data/parity blocks. E.g., b8 is missing while 2 b0 exist:
> b0, b1, b2, b3, b4, b5, b6, b7, b0
> If the NameNode keeps running, NN is able to detect the duplication of b0 and
> will put the block into the excess map. {{countNodes}} excludes internal
> blocks captured in the excess map thus can return the correct number of live
> replicas. However, if NN restarts before sending out the reconstruction
> command, the missing internal block cannot be detected anymore. The following
> steps can reproduce the issue:
> # create an EC file
> # kill DN1 and wait for the reconstruction to happen
> # start DN1 again
> # kill DN2 and restart NN immediately
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