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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1606) Provide a stronger data guarantee in the write pipeline
Date Fri, 11 Feb 2011 03:41:57 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12993330#comment-12993330
] 

Tsz Wo (Nicholas), SZE commented on HDFS-1606:
----------------------------------------------

Below are the proposed new configuration properties.
{code:xml}
<property>
  <name>dfs.client.block.write.replace-datanode-on-failure.enable</name>
  <value>ture</value>
  <description>
    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.  The feature is
    to add new datanodes to the pipeline.

    This is a site-wise property to enable/disable the feature.

    See also dfs.client.block.write.replace-datanode-on-failure.policy
  </description>
</property>

<property>
  <name>dfs.client.block.write.replace-datanode-on-failure.policy</name>
  <value>DEFAULT</value>
  <description>
    This property is used only if the value of
    dfs.client.block.write.replace-datanode-on-failure.enable is true.

    ALWAYS: always add a new datanode when an existing datanode is removed.
    
    NEVER: never add a new datanode.

    DEFAULT: add a new datanode only if
             (1) the number of datanodes in the pipeline drops from 2 to 1; or
             (2) the block is reopened for append.
  </description>
</property>
{code}

> 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
>         Attachments: h1606_20110210.patch
>
>
> 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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