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https://issues.apache.org/jira/browse/HDFS-503?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13060975#comment-13060975
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dhruba borthakur commented on HDFS-503:
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1. Raid has no impact on dfsadmin -report command.
2. You won't be able to set a replication factor to 0. You would have to
manually pull the plug (kill it) on a datanode to see how raid works.
3. stripe locations do not contribute to split locations of a block, thus they
are not used for map-reduce locality.
> Implement erasure coding as a layer on HDFS
> -------------------------------------------
>
> Key: HDFS-503
> URL: https://issues.apache.org/jira/browse/HDFS-503
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: contrib/raid
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Fix For: 0.21.0
>
> Attachments: raid1.txt, raid2.txt
>
>
> The goal of this JIRA is to discuss how the cost of raw storage for a HDFS
> file system can be reduced. Keeping three copies of the same data is very
> costly, especially when the size of storage is huge. One idea is to reduce
> the replication factor and do erasure coding of a set of blocks so that the
> over probability of failure of a block remains the same as before.
> Many forms of error-correcting codes are available, see
> http://en.wikipedia.org/wiki/Erasure_code. Also, recent research from CMU has
> described DiskReduce
> https://opencirrus.org/system/files/Gibson-OpenCirrus-June9-09.ppt.
> My opinion is to discuss implementation strategies that are not part of base
> HDFS, but is a layer on top of HDFS.
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