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https://issues.apache.org/jira/browse/HDFS-2825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14248733#comment-14248733
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Nathan Roberts commented on HDFS-2825:
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[~tlipcon] - It might help. I'm a little concerned about the additional round
trip and how we might enable it globally for an entire cluster. We'll be
running some experiments with a global config for the block placement policy,
and then go from there.
> Add test hook to turn off the writer preferring its local DN
> ------------------------------------------------------------
>
> Key: HDFS-2825
> URL: https://issues.apache.org/jira/browse/HDFS-2825
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 0.23.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Minor
> Fix For: 0.24.0, 0.23.1
>
> Attachments: hdfs-2825.txt, hdfs-2825.txt
>
>
> Currently, the default block placement policy always places the first replica
> in the pipeline on the local node if there is a valid DN running there. In
> some network designs, within-rack bandwidth is never constrained so this
> doesn't give much of an advantage. It would also be really useful to disable
> this for MiniDFSCluster tests, since currently if you start a multi-DN
> cluster and write with replication level 1, all of the replicas go to the
> same DN.
> _[per discussion below, this was changed to not add a config, but only to add
> a hook for testing]_
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