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From "Andrew Wang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10530) BlockManager reconstruction work scheduling should correctly adhere to EC block placement policy
Date Wed, 22 Mar 2017 01:03:41 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10530?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15935602#comment-15935602
] 

Andrew Wang commented on HDFS-10530:
------------------------------------

Oh, interesting! Thanks for digging in Manoj.

If there are three DNs each doing reconstruction, that's less efficient since it does 3*num_data_blocks
of network reads, vs. having 1 DN do num_data_blocks to make all three missing blocks, and
copying two to other DNs. Also something to investigate.

> BlockManager reconstruction work scheduling should correctly adhere to EC block placement
policy
> ------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-10530
>                 URL: https://issues.apache.org/jira/browse/HDFS-10530
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: Rui Gao
>            Assignee: Manoj Govindassamy
>              Labels: hdfs-ec-3.0-nice-to-have
>             Fix For: 3.0.0-alpha3
>
>         Attachments: HDFS-10530.1.patch, HDFS-10530.2.patch, HDFS-10530.3.patch, HDFS-10530.4.patch,
HDFS-10530.5.patch
>
>
> This issue was found by [~tfukudom].
> Under RS-DEFAULT-6-3-64k EC policy, 
> 1. Create an EC file, the file was witten to all the 5 racks( 2 dns for each) of the
cluster.
> 2. Reconstruction work would be scheduled if the 6th rack is added. 
> 3. While adding the 7th rack or more racks will not trigger reconstruction work. 
> Based on default EC block placement policy defined in “BlockPlacementPolicyRackFaultTolerant.java”,
EC file should be able to be scheduled to distribute to 9 racks if possible.
> In *BlockManager#isPlacementPolicySatisfied(BlockInfo storedBlock)* , *numReplicas* of
striped blocks might should be *getRealTotalBlockNum()*, instead of *getRealDataBlockNum()*.



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