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From "Rodrigo Schmidt (JIRA)" <j...@apache.org>
Subject [jira] Commented: (MAPREDUCE-1831) Delete the co-located replicas when raiding file
Date Fri, 18 Jun 2010 21:54:26 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-1831?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12880339#action_12880339
] 

Rodrigo Schmidt commented on MAPREDUCE-1831:
--------------------------------------------

This still has the problem of probably leaving both replicas on the same switch, right?

> 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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