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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-86) Corrupted blocks get deleted but not replicated
Date Thu, 19 Aug 2010 16:58:17 GMT

    [ https://issues.apache.org/jira/browse/HDFS-86?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12900357#action_12900357

Hairong Kuang commented on HDFS-86:

This jira is too old. It should be closed.

Now HDFS has a different policy with corrupt replicas. A corrupt replica does not get deleted
until a good replica gets replicated. 

The problem you have is caused by the 2-node cluster. Because it does not an extra node to
place the good replica, the corrupt one never gets deleted. If you add one more node to the
cluster, the problem will go away. 

> 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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