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https://issues.apache.org/jira/browse/MAPREDUCE-1831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12882225#action_12882225
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Scott Chen commented on MAPREDUCE-1831:
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Thanks, Dhruba. Yes, this one makes sense only when MAPREDUCE-1861 is available.
> Delete the co-located replicas when raiding file
> ------------------------------------------------
>
> Key: MAPREDUCE-1831
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1831
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: contrib/raid
> Affects Versions: 0.22.0
> Reporter: Scott Chen
> Assignee: Scott Chen
> Fix For: 0.22.0
>
> Attachments: MAPREDUCE-1831.20100610.txt, MAPREDUCE-1831.txt,
> MAPREDUCE-1831.v1.1.txt
>
>
> In raid, it is good to have the blocks on the same stripe located on
> different machine.
> This way when one machine is down, it does not broke two blocks on the stripe.
> By doing this, we can decrease the block error probability in raid from
> O(p^3) to O(p^4) which can be a hugh improvement (where p is the replica
> missing probability).
> One way to do this is that we can add a new BlockPlacementPolicy which
> deletes the replicas that are co-located.
> So when raiding the file, we can make the remaining replicas live on
> different machines.
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