Chris Nauroth created HDFS-8432:
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Summary: Introduce a minimum compatible layout version to allow
downgrade in more rolling upgrade use cases.
Key: HDFS-8432
URL: https://issues.apache.org/jira/browse/HDFS-8432
Project: Hadoop HDFS
Issue Type: Improvement
Components: namenode, rolling upgrades
Reporter: Chris Nauroth
Assignee: Chris Nauroth
Maintain the prior layout version during the upgrade window and reject attempts
to use new features until after the upgrade has been finalized. This
guarantees that the prior software version can read the fsimage and edit logs
if the administrator decides to downgrade. This will make downgrade usable for
the majority of NameNode layout version changes, which just involve
introduction of new edit log operations.
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