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https://issues.apache.org/jira/browse/HDFS-2936?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13277219#comment-13277219
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Eli Collins commented on HDFS-2936:
-----------------------------------
bq. For instance, I create file with 3-rep, but get only 2 DNs in pipeline due
to load or failure for my block writes, then when I call close(), it will hang
infinitely cause there's only two replicas.
So the bug here isn't that we need a better way to specify an hdfs-wide min
replication - we already have dfs.namenode.replication.min. Seems like this is
a bug, close shouldn't hang if we have fewer than dfs.namenode.replication.min
replicas.
> Provide a better way to specify a HDFS-wide minimum replication requirement
> ---------------------------------------------------------------------------
>
> 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
> Attachments: HDFS-2936.patch
>
>
> 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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