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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-7646) HDFS truncate may remove data from the supposedly read-only previous/ directory during an upgrade
Date Tue, 20 Jan 2015 21:31:34 GMT
Colin Patrick McCabe created HDFS-7646:
------------------------------------------

             Summary: HDFS truncate may remove data from the supposedly read-only previous/
directory during an upgrade
                 Key: HDFS-7646
                 URL: https://issues.apache.org/jira/browse/HDFS-7646
             Project: Hadoop HDFS
          Issue Type: Bug
            Reporter: Colin Patrick McCabe
            Priority: Blocker


During a DataNode layout version upgrade, HDFS creates hardlinks.  These hardlinks allow the
same block to be accessible from both the current/ and previous/ directories.  Rollback is
possible by deleting the current/ directory and renaming previous/ to current/.

However, if the user truncates one of these hardlinked block files, it effectively eliminates
the ability to roll back to the previous data.

We probably need to disable truncation-in-place during a DataNode upgrade.



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