[jira] [Commented] (HDFS-7787) Split QUEUE_HIGHEST_PRIORITY in UnderReplicatedBlocks to give more priority to blocks on nodes being decomissioned

["Frode Halvorsen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-7787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14321709#comment-14321709 ] 

Frode Halvorsen commented on HDFS-7787:
---------------------------------------

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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