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https://issues.apache.org/jira/browse/HDFS-6981?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14126539#comment-14126539
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Haohui Mai commented on HDFS-6981:
----------------------------------
+1
> 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,
> HDFS-6981.03.patch, HDFS-6981.04.patch, HDFS-6981.05.patch,
> HDFS-6981.06.patch, HDFS-6981.07.patch, HDFS-6981.08.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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