Colin Patrick McCabe created HDFS-7646:
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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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