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From "stack (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, 21 Mar 2016 23:15:25 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3702?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15205343#comment-15205343
] 

stack commented on HDFS-3702:
-----------------------------

bq. Hi stack, the attribute could be set by an installer script or an API call at process
startup

 [~arpitagarwal]Thanks. Yeah, vendors could ensure installers set the attribute. There are
a significant set of installs where HBase shows up post-HDFS install and/or where HBase does
not have sufficient permissions to set attributes on HDFS. I don't know the percentage. Would
be just easier all around if it could be managed internally by HBase so no need to get scripts
and/or operators involved. 

bq. ...so if you think HBase needs a solution now, ...

Smile. The issue was opened in July 2012 so we not holding our breath (smile). Would be cool
if we could ask HDFS to not write local. Anyone doing WAL-on-HDFS will appreciate this in
HDFS.

Thanks [~arpitagarwal]

> 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: 2.5.1
>            Reporter: Nicolas Liochon
>            Assignee: Lei (Eddy) Xu
>            Priority: Minor
>              Labels: BB2015-05-TBR
>         Attachments: HDFS-3702.000.patch, HDFS-3702.001.patch, HDFS-3702.002.patch, HDFS-3702.003.patch,
HDFS-3702.004.patch, HDFS-3702.005.patch, HDFS-3702.006.patch, HDFS-3702.007.patch, HDFS-3702.008.patch,
HDFS-3702_Design.pdf
>
>
> 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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