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From "Andrew Purtell (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3743) QJM: improve formatting behavior for JNs
Date Tue, 31 Jul 2012 18:16:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13425982#comment-13425982
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Andrew Purtell commented on HDFS-3743:
--------------------------------------

Not sure about the notion of automating an "unsafe startup" in the case the majority of JNs
are unformatted. What if instead, it's possible to start up the NN in recovery mode and have
it interactively suggest actions including initializing the unformatted JNs? Could summarize
the most recent txn (or a few txns) of the available logs before asking which txid to choose
as latest?
                
> 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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