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https://issues.apache.org/jira/browse/HDFS-2139?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17867676#comment-17867676
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liuguanghua commented on HDFS-2139:
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-- We already has hadoop distcp, Why do we need hdfs dfs -distcp?
[~zeekling] , dfs -fastcp command like dfs -cp , and distcp is a mapreduce
program and reply on yarn. For some case, we can use fastcp without distcp
with only hdfs usage.
> Fast copy for HDFS.
> -------------------
>
> Key: HDFS-2139
> URL: https://issues.apache.org/jira/browse/HDFS-2139
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Pritam Damania
> Assignee: Rituraj
> Priority: Major
> Labels: pull-request-available
> Attachments: HDFS-2139-For-2.7.1.patch, HDFS-2139.patch,
> HDFS-2139.patch, image-2022-08-11-11-48-17-994.png
>
> Original Estimate: 168h
> Remaining Estimate: 168h
>
> There is a need to perform fast file copy on HDFS. The fast copy mechanism
> for a file works as
> follows :
> 1) Query metadata for all blocks of the source file.
> 2) For each block 'b' of the file, find out its datanode locations.
> 3) For each block of the file, add an empty block to the namesystem for
> the destination file.
> 4) For each location of the block, instruct the datanode to make a local
> copy of that block.
> 5) Once each datanode has copied over its respective blocks, they
> report to the namenode about it.
> 6) Wait for all blocks to be copied and exit.
> This would speed up the copying process considerably by removing top of
> the rack data transfers.
> Note : An extra improvement, would be to instruct the datanode to create a
> hardlink of the block file if we are copying a block on the same datanode
> [~xuzq_zander]Provided a design doc
> https://docs.google.com/document/d/1uGHA2dXLldlNoaYF-4c63baYjCuft_T88wdvhwVgh6c/edit?usp=sharing
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