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https://issues.apache.org/jira/browse/HDFS-13356?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16448932#comment-16448932
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Konstantin Shvachko commented on HDFS-13356:
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+1 looks good.
> Balancer:Set default value of minBlockSize to 10mb
> ---------------------------------------------------
>
> Key: HDFS-13356
> URL: https://issues.apache.org/jira/browse/HDFS-13356
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: balancer & mover
> Affects Versions: 2.7.5
> Reporter: Bharat Viswanadham
> Assignee: Bharat Viswanadham
> Priority: Major
> Labels: balancer, upgrades
> Attachments: HDFS-13356.00.patch, HDFS-13356.01.patch,
> HDFS-13356.02.patch
>
>
> It seems we can run into a problem while a rolling upgrade with this.
> The Balancer is upgraded after NameNodes, so once NN is upgraded it will
> expect {{minBlockSize}} parameter in {{getBlocks()}}. The Balancer cannot
> send it yet, so NN will use the default, which you set to 0. So NN will start
> unexpectedly sending small blocks to the Balancer. So we should
> # either change the default in protobuf to 10 MB
> # or treat {{minBlockSize == 0}} in {{NameNodeRpcServer}} as a signal to use
> the configuration variable
> {{DFSConfigKeys.DFS_BALANCER_GETBLOCKS_MIN_BLOCK_SIZE_KEY}}.
> If you agree, we should create a follow up jira. I wanted to backport this
> down the chain of branches, but this upgrade scenario is stopping me.
> [~shv] commented this in HDFS-13222 jira.
> https://issues.apache.org/jira/browse/HDFS-13222?focusedCommentId=16414855&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-16414855
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