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From "Thanh Do (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-86) Corrupted blocks get deleted but not replicated
Date Thu, 19 Aug 2010 16:30:17 GMT

    [ https://issues.apache.org/jira/browse/HDFS-86?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12900342#action_12900342

Thanh Do commented on HDFS-86:

i have a cluster of two nodes. Say a block with 2 replicas, and one of them get corrupted.
The corrupted block is reported to NN, but it is never deleted or replicated, even after NN
Not sure this is a bug or just a policy.
I am playing the append-trunk

> Corrupted blocks get deleted but not replicated
> -----------------------------------------------
>                 Key: HDFS-86
>                 URL: https://issues.apache.org/jira/browse/HDFS-86
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Hairong Kuang
>            Assignee: Hairong Kuang
>         Attachments: blockInvalidate.patch
> When I test the patch to HADOOP-1345 on a two node dfs cluster, I see that dfs correctly
delete the corrupted replica and successfully retry reading from the other correct replica,
but the block does not get replicated. The block remains with only 1 replica until the next
block report comes in.
> In my testcase, since the dfs cluster has only 2 datanodes, the target of replication
is the same as the target of block invalidation.  After poking the logs, I found out that
the namenode sent the replication request before the block invalidation request. 
> This is because the namenode does not invalidate a block well. In FSNamesystem.invalidateBlock,
it first puts the invalidate request in a queue and then immediately removes the replica from
its state, which triggers the choosing a target for the block. When requests are sent back
to the target datanode as a reply to a heartbeat message, the replication requests have higher
priority than the invalidate requests.
> This problem could be solved if a namenode removes an invalidated replica from its state
only after the invalidate request is sent to the datanode.

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