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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-6800) Detemine how Datanode layout changes should interact with rolling upgrade
Date Fri, 01 Aug 2014 00:29:40 GMT
Colin Patrick McCabe created HDFS-6800:
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             Summary: Detemine how Datanode layout changes should interact with rolling upgrade
                 Key: HDFS-6800
                 URL: https://issues.apache.org/jira/browse/HDFS-6800
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: datanode
    Affects Versions: 2.6.0
            Reporter: Colin Patrick McCabe


We need to handle attempts to rolling-upgrade the DataNode to a new storage directory layout.

One approach is to disallow such upgrades.  If we choose this approach, we should make sure
that the system administrator gets a helpful error message and a clean failure when trying
to use rolling upgrade to a version that doesn't support it.  Based on the compatibility guarantees
described in HDFS-5535, this would mean that *any* future DataNode layout changes would require
a major version upgrade.

Another approach would be to support rolling upgrade from an old DN storage layout to a new
layout.  This approach requires us to change our documentation to explain to users that they
should supply the {{\-rollback}} command on the command-line when re-starting the DataNodes
during rolling rollback.  Currently the documentation just says to restart the DataNode normally.

Another issue here is that the DataNode's usage message describes rollback options that no
longer exist.  The help text says that the DN supports {{\-rollingupgrade rollback}}, but
this option was removed by HDFS-6005.



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