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https://issues.apache.org/jira/browse/HDFS-3672?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13418911#comment-13418911
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Suresh Srinivas commented on HDFS-3672:
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bq. Currently, HDFS exposes on which datanodes a block resides, which allows
clients to make scheduling decisions for locality and load balancing. Extending
this to also expose on which disk on a datanode a block resides would enable
even better scheduling, on a per-disk rather than coarse per-datanode basis.
I am not sure I understand your motivation. I can see Namenode understanding
disk/storages in Datanode for improving the scheduling. I am not sure why
clients should be exposed to this information. Can you describe use cases more
clearly. Also please attach a short writeup/design that summarizes the
motivation that captures these discussion as design.
As regards NN knowing about this information, that is one of the motivations of
HDFS-2832. If each storage volume that corresponds to a disk on Datanode has a
separate storage ID, NN gets block reports and other stats per disk.
> Expose disk-location information for blocks to enable better scheduling
> -----------------------------------------------------------------------
>
> Key: HDFS-3672
> URL: https://issues.apache.org/jira/browse/HDFS-3672
> Project: Hadoop HDFS
> Issue Type: Improvement
> Affects Versions: 2.0.0-alpha
> Reporter: Andrew Wang
> Assignee: Andrew Wang
> Attachments: hdfs-3672-1.patch
>
>
> Currently, HDFS exposes on which datanodes a block resides, which allows
> clients to make scheduling decisions for locality and load balancing.
> Extending this to also expose on which disk on a datanode a block resides
> would enable even better scheduling, on a per-disk rather than coarse
> per-datanode basis.
> This API would likely look similar to Filesystem#getFileBlockLocations, but
> also involve a series of RPCs to the responsible datanodes to determine disk
> ids.
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