[jira] Resolved: (HDFS-795) DFS Write pipeline does not detect defective datanode correctly in some cases (HADOOP-3339)

["Todd Lipcon (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-795?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Todd Lipcon resolved HDFS-795.
------------------------------

    Resolution: Duplicate

HDFS-101 duplicates this, and fix is under way there.

> DFS Write pipeline does not detect defective datanode correctly in some cases (HADOOP-3339)
> -------------------------------------------------------------------------------------------
>
>                 Key: HDFS-795
>                 URL: https://issues.apache.org/jira/browse/HDFS-795
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs client
>    Affects Versions: 0.20.1
>            Reporter: Raghu Angadi
>            Priority: Critical
>             Fix For: 0.20.2
>
>         Attachments: toreproduce-5796.patch
>
>
> HDFS write pipeline does not select the correct datanode in some error cases. One example : say DN2 is the second datanode and write to it times out since it is in a bad state.. pipeline actually removes the first datanode. If such a datanode happens to be the last one in the pipeline, write is aborted completely with a hard error.
> Essentially the error occurs when writing to a downstream datanode fails rather than reading. This bug was actually fixed in 0.18 (HADOOP-3339). But HADOOP-1700 essentially reverted it. I am not sure why.
> It is absolutely essential for HDFS to handle failures on subset of datanodes in a pipeline. We should not have at least known bugs that lead to hard failures.
> I will attach patch for a hack that illustrates this problem. Still thinking of how an automated test would look like for this one. 
> My preferred target for  this fix is 0.20.1.

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