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https://issues.apache.org/jira/browse/HDFS-9083?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14979126#comment-14979126
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Rushabh S Shah commented on HDFS-9083:
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[~kihwal]: Thanks for committing.
> Replication violates block placement policy.
> --------------------------------------------
>
> Key: HDFS-9083
> URL: https://issues.apache.org/jira/browse/HDFS-9083
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: HDFS, namenode
> Affects Versions: 2.6.0
> Reporter: Rushabh S Shah
> Assignee: Rushabh S Shah
> Priority: Blocker
> Fix For: 2.7.2
>
> Attachments: HDFS-9083-branch-2.7.patch
>
>
> Recently we are noticing many cases in which all the replica of the block are
> residing on the same rack.
> During the block creation, the block placement policy was honored.
> But after node failure event in some specific manner, the block ends up in
> such state.
> On investigating more I found out that BlockManager#blockHasEnoughRacks is
> dependent on the config (net.topology.script.file.name)
> {noformat}
> if (!this.shouldCheckForEnoughRacks) {
> return true;
> }
> {noformat}
> We specify DNSToSwitchMapping implementation (our own custom implementation)
> via net.topology.node.switch.mapping.impl and no longer use
> net.topology.script.file.name config.
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