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https://issues.apache.org/jira/browse/HDFS-7891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14383187#comment-14383187
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Walter Su commented on HDFS-7891:
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If we put 2 replicas on local rack during file creation, 1 LN + 1 LR + RR_1 +
RR_2 + RR_3 + RR_4..... Only local rack is allowed 2 replica, and remote rack
is allowed 1 replica. We can tolerant 2 racks failure(out of 8 racks). It
reduces 1 rack traffic during file creation, but will not during Reconstruction.
If we put 2 replicas on every racks during file creation and Reconstruction. 1
LN + 1 LR + RR_1 + RR_1 + RR_2 + RR_2. Both file creation and Reconstruction
process can reduce 1 rack traffic. We can tolerant 1 rack failure(out of 4
racks).
The default policy can tolerant 1 rack failure(out of 2 racks).
> 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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