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From "Hudson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-13788) Update EC documentation about rack fault tolerance
Date Tue, 14 Aug 2018 19:42:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-13788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16580332#comment-16580332
] 

Hudson commented on HDFS-13788:
-------------------------------

SUCCESS: Integrated in Jenkins build Hadoop-trunk-Commit #14769 (See [https://builds.apache.org/job/Hadoop-trunk-Commit/14769/])
HDFS-13788. Update EC documentation about rack fault tolerance. (xiao: rev cede33997f7ab09fc046017508b680e282289ce3)
* (edit) hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSErasureCoding.md


> Update EC documentation about rack fault tolerance
> --------------------------------------------------
>
>                 Key: HDFS-13788
>                 URL: https://issues.apache.org/jira/browse/HDFS-13788
>             Project: Hadoop HDFS
>          Issue Type: Task
>          Components: documentation, erasure-coding
>    Affects Versions: 3.0.0
>            Reporter: Xiao Chen
>            Assignee: Kitti Nanasi
>            Priority: Major
>             Fix For: 3.2.0, 3.0.4, 3.1.2
>
>         Attachments: HDFS-13788.001.patch, HDFS-13788.002.patch
>
>
> From http://hadoop.apache.org/docs/r3.0.0/hadoop-project-dist/hadoop-hdfs/HDFSErasureCoding.html:
> {quote}
> For rack fault-tolerance, it is also important to have at least as many racks as the
configured EC stripe width. For EC policy RS (6,3), this means minimally 9 racks, and ideally
10 or 11 to handle planned and unplanned outages. For clusters with fewer racks than the stripe
width, HDFS cannot maintain rack fault-tolerance, but will still attempt to spread a striped
file across multiple nodes to preserve node-level fault-tolerance.
> {quote}
> Theoretical minimum is 3 racks, and ideally 9 or more, so the document should be updated.
> (I didn't check timestamps, but this is probably due to {{BlockPlacementPolicyRackFaultTolerant}}
isn't completely done when HDFS-9088 introduced this doc. Later there's also examples in {{TestErasureCodingMultipleRacks}}
to test this explicitly.)



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