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From "Harsh J (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-2936) Provide a better way to specify a HDFS-wide minimum replication requirement
Date Fri, 10 Feb 2012 21:51:02 GMT
Provide a better way to specify a HDFS-wide minimum replication requirement
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                 Key: HDFS-2936
                 URL: https://issues.apache.org/jira/browse/HDFS-2936
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: name-node
    Affects Versions: 0.23.0
            Reporter: Harsh J
            Assignee: Harsh J


Currently, if an admin would like to enforce a replication factor for all files on his HDFS,
he does not have a way. He may arguably set dfs.replication.min but that is a very hard guarantee
and if the pipeline can't afford that number for some reason/failure, the close() does not
succeed on the file being written and leads to several issues.

After discussing with Todd, we feel it would make sense to introduce a second config (which
is ${dfs.replication.min} by default) which would act as a minimum specified replication for
files. This is different than dfs.replication.min which also ensures that many replicas are
recorded before completeFile() returns... perhaps something like ${dfs.replication.min.user}.
We can leave dfs.replication.min alone for hard-guarantees and add ${dfs.replication.min.for.block.completion}
which could be left at 1 even if dfs.replication.min is >1, and let files complete normally
but not be of a low replication factor (so can be monitored and accounted-for later).

I'm prefering the second option myself. Will post a patch with tests soon.

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