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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