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https://issues.apache.org/jira/browse/HDFS-7891?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14387629#comment-14387629
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Tsz Wo Nicholas Sze commented on HDFS-7891:
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First of all, the "best fault tolerance" is for improving rack failure
tolerance but not for other case. If you agree, we should as well update the
summary of this JIRA.
For rack failure, although it does happen but is uncommon. Also, when a rack
fails, the data stored under the rack is only temporarily unavailable but not
permanently lost.
For replication==3, we store block replicas only in two different racks. It
there are two racks failed at the same time. Some data is unavailable. We
should do the same thing for EC blocks.
I don't object adding the new 1 ec block per rack policy here but I believe the
default policy should allow max 2 ec blocks per rack instead of 1.
> 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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