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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-900) Corrupt replicas are not tracked correctly through block report from DN
Date Wed, 24 Nov 2010 20:24:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-900?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12935471#action_12935471
] 

Todd Lipcon commented on HDFS-900:
----------------------------------

Yes, I believe this reproduces in 0.21 and 0.22 (the to-reproduce.patch was against trunk
at the time though likely is out of date now)

> Corrupt replicas are not tracked correctly through block report from DN
> -----------------------------------------------------------------------
>
>                 Key: HDFS-900
>                 URL: https://issues.apache.org/jira/browse/HDFS-900
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 0.22.0
>            Reporter: Todd Lipcon
>            Priority: Critical
>         Attachments: log-commented, to-reproduce.patch
>
>
> This one is tough to describe, but essentially the following order of events is seen
to occur:
> # A client marks one replica of a block to be corrupt by telling the NN about it
> # Replication is then scheduled to make a new replica of this node
> # The replication completes, such that there are now 3 good replicas and 1 corrupt replica
> # The DN holding the corrupt replica sends a block report. Rather than telling this DN
to delete the node, the NN instead marks this as a new *good* replica of the block, and schedules
deletion on one of the good replicas.
> I don't know if this is a dataloss bug in the case of 1 corrupt replica with dfs.replication=2,
but it seems feasible. I will attach a debug log with some commentary marked by '============>',
plus a unit test patch which I can get to reproduce this behavior reliably. (it's not a proper
unit test, just some edits to an existing one to show it)

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