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https://issues.apache.org/jira/browse/HDFS-7891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14383140#comment-14383140
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Walter Su commented on HDFS-7891:
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{quote}
The current BlockPlacementPolicyDefault looks like LN+RR_1+RR_1
{quote}
Yes, it is. The traffic of LN+RR_1+RR_1 is the same as LN + LR +RR_1. The
former is better than the latter because when the replica factor is 2, two
replica will be placed in LN+RR_1. But The numOfTargets that EC group chooses
apparently bigger than 2.
I think Nicholas is trying to say, we can cut down one inter-rack traffic.
> A block placement policy with best fault tolerance
> --------------------------------------------------
>
> Key: HDFS-7891
> URL: https://issues.apache.org/jira/browse/HDFS-7891
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Reporter: Walter Su
> Assignee: Walter Su
> Attachments: HDFS-7891.002.patch, HDFS-7891.003.patch,
> HDFS-7891.004.patch, HDFS-7891.patch, PlacementPolicyBenchmark.txt,
> testresult.txt
>
>
> a block placement policy tries its best to place replicas to most racks.
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