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Date: Mon, 1 Sep 2014 21:41:20 +0000 (UTC)
From: "Arpit Agarwal (JIRA)" <jira@apache.org>
To: hdfs-dev@hadoop.apache.org
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Subject: [jira] [Created] (HDFS-6981) DN upgrade with layout version change
 should not use trash
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Arpit Agarwal created HDFS-6981:
-----------------------------------

             Summary: 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


Post HDFS-6800, we can encounter the following scenario:
# We start with DN software version -55 and initiate a rolling upgrade to v=
ersion -56
# We delete some blocks, and they are moved to trash
# We roll back to DN software version -55 using the -rollback flag =E2=80=
=93 since we are running the old code (prior to this patch), we will restor=
e 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 =E2=80=93=
 since the trash still exists, it will be restored at this point, the appen=
ded-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 h=
ave a previous directory.

Thanks to [~james.thomas] for reporting this.


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