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https://issues.apache.org/jira/browse/HDFS-3256?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252240#comment-13252240
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Todd Lipcon commented on HDFS-3256:
-----------------------------------
I think there's an issue here with safemode's delayed initialization of repl
queues. As the DNs are checking in, when the cluster transitions from
single-rack to multi-rack, it will call processMisReplicatedBlocks, even if the
threshold (DFS_NAMENODE_REPL_QUEUE_THRESHOLD_PCT_KEY) hasn't been crossed. I
think you need to somehow tie this back to the flag in safemode which
determines whether misreplicated blocks have been processed yet.
> HDFS considers blocks under-replicated if topology script is configured with
> only 1 rack
> ----------------------------------------------------------------------------------------
>
> Key: HDFS-3256
> URL: https://issues.apache.org/jira/browse/HDFS-3256
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.0.0
> Reporter: Aaron T. Myers
> Assignee: Aaron T. Myers
> Attachments: HDFS-3256.patch, HDFS-3256.patch
>
>
> HDFS treats the mere presence of a topology script being configured as
> evidence that there are multiple racks. If there is in fact only a single
> rack, the NN will try to place the blocks on at least two racks, and thus
> blocks will be considered to be under-replicated.
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