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https://issues.apache.org/jira/browse/HDFS-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12991321#comment-12991321
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Tsz Wo (Nicholas), SZE commented on HDFS-1606:
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Below are some steps for adding a datanode to a pipeline:
# Find a datanode _D_ by some means.
# Add _D_ to the existing pipeline.
# Continue writing.
# Close the pipeline.

\\
Moreover, we have to:
\(*) Transfer the existing data to _D_.

The question is where to put \(*)?

> Provide a stronger data guarantee in the write pipeline
> -------------------------------------------------------
>
>                 Key: HDFS-1606
>                 URL: https://issues.apache.org/jira/browse/HDFS-1606
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: data-node, hdfs client
>            Reporter: Tsz Wo (Nicholas), SZE
>            Assignee: Tsz Wo (Nicholas), SZE
>
> In the current design, if there is a datanode/network failure in the write 
> pipeline, DFSClient will try to remove the failed datanode from the pipeline 
> and then continue writing with the remaining datanodes.  As a result, the 
> number of datanodes in the pipeline is decreased.  Unfortunately, it is 
> possible that DFSClient may incorrectly remove a healthy datanode but leave 
> the failed datanode in the pipeline because failure detection may be 
> inaccurate under erroneous conditions.
> We propose to have a new mechanism for adding new datanodes to the pipeline 
> in order to provide a stronger data guarantee.

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