Todd Lipcon created HDFS-3743:
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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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