[jira] [Work started] (HDFS-6981) DN upgrade with layout version change should not use trash

["Arpit Agarwal (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HDFS-6981?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Work on HDFS-6981 started by Arpit Agarwal.
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> 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
>
> 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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