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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4832) Namenode doesn't change the number of missing blocks in safemode when DNs rejoin
Date Fri, 17 May 2013 20:05:16 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4832?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13660996#comment-13660996
] 

Kihwal Lee commented on HDFS-4832:
----------------------------------

SBN also skips processing of over/under replicated blocks. The new condition in your patch
will change SBN's behavior. 

There is another aspect of this issue. Since {{neededReplications}} is not scanned in safe
mode and on SBN, orphaned blocks in there cause problems during {{metaSave()}}. They normally
go away when ReplicationMonitor generates DN work, but since it doesn't happen while in these
modes, those blocks can linger. When {{metaSave()}} hits one of these blocks, it dies with
NPE because there is no corresponding {{INodeFile}}.


                
> Namenode doesn't change the number of missing blocks in safemode when DNs rejoin
> --------------------------------------------------------------------------------
>
>                 Key: HDFS-4832
>                 URL: https://issues.apache.org/jira/browse/HDFS-4832
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 3.0.0, 0.23.7, 2.0.5-beta
>            Reporter: Ravi Prakash
>            Assignee: Ravi Prakash
>            Priority: Critical
>         Attachments: HDFS-4832.patch
>
>
> Courtesy Karri VRK Reddy!
> {quote}
> 1. Namenode lost datanodes causing missing blocks
> 2. Namenode was put in safe mode
> 3. Datanode restarted on dead nodes 
> 4. Waited for lots of time for the NN UI to reflect the recovered blocks.
> 5. Forced NN out of safe mode and suddenly,  no more missing blocks anymore.
> {quote}
> I was able to replicate this on 0.23 and trunk. I set dfs.namenode.heartbeat.recheck-interval
to 1 and killed the DN to simulate "lost" datanode.
> Without the NN updating this list of missing blocks, the grid admins will not know when
to take the cluster out of safemode.

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