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From "Sameer Paranjpye (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 18:24:04 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-1557?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12509636
] 

Sameer Paranjpye commented on HADOOP-1557:
------------------------------------------

Why not have clients and/or datanodes report corrupt replicas to the Namenode? Is this not
already done?

The Namenode should remove and replace corrupt replicas when they are reported by clients/datanodes,
probably on read to start off with. This can be subsequently enhanced to to periodic block
scanning.

> 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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