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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-6005) Simplify Datanode rollback and downgrade
Date Mon, 24 Feb 2014 14:47:20 GMT
Suresh Srinivas created HDFS-6005:

             Summary: Simplify Datanode rollback and downgrade
                 Key: HDFS-6005
                 URL: https://issues.apache.org/jira/browse/HDFS-6005
             Project: Hadoop HDFS
          Issue Type: Sub-task
          Components: datanode, namenode
            Reporter: Suresh Srinivas
            Assignee: Suresh Srinivas

When rolling upgrade fails, the cluster can either be downgraded or rolled back. With the
current functionality in this feature branch, it is possible to downgrade namenode, while
datanode is incorrectly rolled back. This does not affect the cluster state. The old blocks
that appear back on the datanode due to rollback will be deleted. Similarly it is also possible
to rollback namenode, while datanode is not rolled back. This can cause problem where old
blocks do not appear back on the datanode and can result in missing blocks.

I propose making the following changes:
During rollback or downgrade, the entire cluster must be restarted. The datanodes always restore
the deleted blocks on restart and go back to trash disabled mode. There is no need for datanodes
to be started up -rollingUpgrade -rollback, anymore.
# On namenode downgrade, the restored blocks are deleted.
# On namenode rollback, the restored blocks will be retained and any newly created blocks
(since the start of rolling upgrade) are deleted.

This is much simpler operationally and solves the problem described above.

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