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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3702) Add an option for NOT writing the blocks locally if there is a datanode on the same box as the client
Date Mon, 23 Jul 2012 22:31:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13420999#comment-13420999
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Aaron T. Myers commented on HDFS-3702:
--------------------------------------

Allowing setting of block placement policy per-file or per-stream is an interesting idea,
but for this specific issue (wanting more remote replicas of the HBase WAL when a DN dies)
how about just setting the replication count for this file to 4 when you open it? You can
already do that per-file today in HDFS.
                
> Add an option for NOT writing the blocks locally if there is a datanode on the same box
as the client
> -----------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-3702
>                 URL: https://issues.apache.org/jira/browse/HDFS-3702
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client
>    Affects Versions: 1.0.3, 2.0.0-alpha
>            Reporter: nkeywal
>            Priority: Minor
>
> This is useful for Write-Ahead-Logs: these files are writen for recovery only, and are
not read when there are no failures.
> Taking HBase as an example, these files will be read only if the process that wrote them
(the 'HBase regionserver') dies. This will likely come from a hardware failure, hence the
corresponding datanode will be dead as well. So we're writing 3 replicas, but in reality only
2 of them are really useful.

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