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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-3962) NN should periodically check writability of 'required' journals
Date Thu, 20 Sep 2012 22:45:07 GMT
Todd Lipcon created HDFS-3962:

             Summary: NN should periodically check writability of 'required' journals
                 Key: HDFS-3962
                 URL: https://issues.apache.org/jira/browse/HDFS-3962
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: ha, name-node
    Affects Versions: 2.0.1-alpha, 3.0.0
            Reporter: Todd Lipcon
            Assignee: Todd Lipcon

Currently, our HA design ensures "write fencing" by having the failover controller call a
fencing script before transitioning a new node to active. However, if the fencing script is
based on storage fencing (and not stonith), there is no _read_ fencing. That is to say, the
old active may continue to believe himself active for an unbounded amount of time, assuming
that it does not try to write to its edit log.

This isn't super problematic, but it would be beneficial for monitoring, etc, to have the
old NN periodically check the writability of any "required" journals, and abort if they become
unwritable, even if there are no writes coming into the system.

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