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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-1557) Deletion of excess replicas should prefer to delete corrupted replicas before deleting valid replicas
Date Mon, 02 Jul 2007 22:13:04 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1557?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12509698
] 

dhruba borthakur commented on HADOOP-1557:
------------------------------------------

The bug is that when a setReplication() command is sent to the NameNode, no data blocks are
being read by the client and/or datanode. A block that was corrupt on the datanode is not
known to the namenode at that time.

> Deletion of excess replicas should prefer to delete corrupted replicas before deleting
valid replicas
> -----------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-1557
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1557
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>            Reporter: dhruba borthakur
>
> Suppose a block has three replicas and two of the replicas are corrupted. If the replication
factor of the file is reduced to 2. The filesystem should preferably delete the two corrupted
replicas, otherwise it could lead to a corrupted file.
> One option would be to make the datanode periodically validate all blocks with their
corresponding CRCs. The other option would be to make the setReplication call validate existing
replicas before deleting excess replicas.

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