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From "Arpit Agarwal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6981) DN upgrade with layout version change should not use trash
Date Thu, 04 Sep 2014 20:33:23 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14121945#comment-14121945
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Arpit Agarwal commented on HDFS-6981:
-------------------------------------

Thanks for reviewing Haohui. Let me look into reflection as you suggested.

Overriding versionSupportsFederation is needed so DN storages avoid calling {{LayoutVersion.supports}},
the override calls {{DataNodeLayoutVersion.supports}} instead.

> DN upgrade with layout version change should not use trash
> ----------------------------------------------------------
>
>                 Key: HDFS-6981
>                 URL: https://issues.apache.org/jira/browse/HDFS-6981
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>    Affects Versions: 3.0.0
>            Reporter: James Thomas
>            Assignee: Arpit Agarwal
>         Attachments: HDFS-6981.01.patch, HDFS-6981.02.patch
>
>
> Post HDFS-6800, we can encounter the following scenario:
> # We start with DN software version -55 and initiate a rolling upgrade to version -56
> # We delete some blocks, and they are moved to trash
> # We roll back to DN software version -55 using the -rollback flag – since we are running
the old code (prior to this patch), we will restore the previous directory but will not delete
the trash
> # We append to some of the blocks that were deleted in step 2
> # We then restart a DN that contains blocks that were appended to – since the trash
still exists, it will be restored at this point, the appended-to blocks will be overwritten,
and we will lose the appended data
> So I think we need to avoid writing anything to the trash directory if we have a previous
directory.
> Thanks to [~james.thomas] for reporting this.



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