[HDFS-7646] HDFS truncate may remove data from the supposedly read-only previous/ directory during an upgrade

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Not A Problem
• Assignee: Unassigned
• Reporter: Colin McCabe
• Created: 20/Jan/15 21:31
• Updated: 21/Jan/15 04:05
• Resolved: 21/Jan/15 04:05

Description

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.