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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3256) HDFS considers blocks under-replicated if topology script is configured with only 1 rack
Date Thu, 12 Apr 2012 06:34:26 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3256?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13252240#comment-13252240
] 

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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