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https://issues.apache.org/jira/browse/HDFS-13788?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16580279#comment-16580279
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Xiao Chen edited comment on HDFS-13788 at 8/14/18 6:59 PM:
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Committed to trunk and branch-3.[0-1].
Thanks Kitti for working on this, and Zsolt for reviewing!
was (Author: xiaochen):
Committed to trunk and branch-3.[0-1]
> 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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