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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1497) Possibility of duplicate blockids if dead-datanodes come back up after corresponding files were deleted
Date Sat, 16 Jun 2007 01:20:26 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1497?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12505420
] 

Raghu Angadi commented on HADOOP-1497:
--------------------------------------

> This case is possibly detected by the Client (using CRC).
Actually with Block-Level CRCs this may not be detected at the client either . Since crc is
per block, a client will silently get wrong data.


> Possibility of duplicate blockids if dead-datanodes come back up after corresponding
files were deleted
> -------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-1497
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1497
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> Suppose a datanode D has a block B that belongs to file F. Suppose the datanode D dies
and the namenode replicates those blocks to other datanodes. No, suppose the user deletes
file F. The namenode removes all the blocks that belonged to file F. Now, suppose a new file
F1 is created and the namenode generates the same blockid B for this new file F1. 
> Suppose the old datanode D comes back to life. Now we have a valid corrupted block B
on datanode D.
> This case is possibly detected by the Client (using CRC). But does HDFS need to handle
this scenario better?

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