[jira] Updated: (HDFS-900) Corrupt replicas are not tracked correctly through block report from DN

["Todd Lipcon (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-900?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Todd Lipcon updated HDFS-900:
-----------------------------

         Priority: Blocker  (was: Critical)
    Fix Version/s: 0.22.0

In discussion with Nigel, we'd like to mark this as blocker pending further investigation. If we determine it's not a regression since 0.20 we'll downgrade priority.

> 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: Blocker
>             Fix For: 0.22.0
>
>         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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