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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3962) NN should periodically check writability of 'required' journals
Date Fri, 21 Sep 2012 00:50:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3962?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13460104#comment-13460104
] 

Todd Lipcon commented on HDFS-3962:
-----------------------------------

Oops, the change in EditLogTailer is unrelated to this patch, it belongs with HDFS-3918.
                
> 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: 3.0.0, 2.0.1-alpha
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-3962.txt
>
>
> 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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