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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-3743) QJM: improve formatting behavior for JNs
Date Tue, 31 Jul 2012 01:06:34 GMT
Todd Lipcon created HDFS-3743:
---------------------------------

             Summary: QJM: improve formatting behavior for JNs
                 Key: HDFS-3743
                 URL: https://issues.apache.org/jira/browse/HDFS-3743
             Project: Hadoop HDFS
          Issue Type: Sub-task
    Affects Versions: QuorumJournalManager (HDFS-3077)
            Reporter: Todd Lipcon
            Assignee: Todd Lipcon


Currently, the JournalNodes automatically format themselves when a new writer takes over,
if they don't have any data for that namespace. However, this has a few problems:
1) if the administrator accidentally points a new NN at the wrong quorum (eg corresponding
to another cluster), it will auto-format a directory on those nodes. This doesn't cause any
data loss, but would be better to bail out with an error indicating that they need to be formatted.
2) if a journal node crashes and needs to be reformatted, it should be able to re-join the
cluster and start storing new segments without having to fail over to a new NN.
3) if 2/3 JNs get accidentally reformatted (eg the mount point becomes undone), and the user
starts the NN, it should fail to start, because it may end up missing edits. If it auto-formats
in this case, the user might have silent "rollback" of the most recent edits.

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