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https://issues.apache.org/jira/browse/HDFS-7787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14321709#comment-14321709
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Frode Halvorsen commented on HDFS-7787:
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Hello.
This was some time ago, and it might be that I didn't have any decommissioning
nodes when I was observing that the namenode didn't prioritize the blocks with
only one replica first. When i look in the logs now, the namenode asks the
decommissioning node to replicate every block to three other nodes, thus I
believe it only get replication-requests for blocks with no live replicas.
This leaves me with the struggle to speed up the process :)
> Split QUEUE_HIGHEST_PRIORITY in UnderReplicatedBlocks to give more priority
> to blocks on nodes being decomissioned
> ------------------------------------------------------------------------------------------------------------------
>
> Key: HDFS-7787
> URL: https://issues.apache.org/jira/browse/HDFS-7787
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: datanode
> Affects Versions: 2.6.0
> Environment: 2 namenodes HA, 6 datanodes in two racks
> Reporter: Frode Halvorsen
> Labels: balance, hdfs, replication-performance
>
> Each file has a setting of 3 replicas. split on different racks.
> After a simulated crash of one rack (shutdown of all nodes, deleted
> data-directory an started nodes) and decommssion of one of the nodes in the
> orther rack the replication does not follow 'normal' rules...
> My cluster has appx 25 mill files, and the one node I now try to decommision
> has 9 millions underreplicated blocks, and 3,5 million blocks with 'no live
> replicas'. After a restart of the node, it starts to replicate both types of
> blocks, but after a while, it only repliates under-replicated blocks with
> other live copies. I would think that the 'normal' way to do this would be to
> make sure that all blocks this node keeps the only copy of, should be the
> first to be replicated/balanced ?
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