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https://issues.apache.org/jira/browse/HDFS-2825?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13191321#comment-13191321
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Todd Lipcon commented on HDFS-2825:
-----------------------------------
This still reuses 99% of the code from the existing policy -- it places the
first replica rack-local and the other two on a separate (but same) rack. It
still takes into account load as well as disk space on all the nodes.
The primary purpose is for unit tests - see HDFS-2826 for example. It is not
meant for general purpose use by users, though as noted in the description
there is potentially a use case.
Adding an entirely new block placement implementation for this purpose is
overkill, since it will duplicate all of the code from the existing one.
> Add config option 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: name-node
> Affects Versions: 0.23.0
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Minor
> Attachments: 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.
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