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Date: Wed, 6 Jun 2007 11:19:26 -0700 (PDT)
From: "Koji Noguchi (JIRA)" <jira@apache.org>
To: hadoop-dev@lucene.apache.org
Subject: [jira] Commented: (HADOOP-1300) deletion of excess replicas does
 not take into account 'rack-locality'
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    [ https://issues.apache.org/jira/browse/HADOOP-1300?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12502015 ] 

Koji Noguchi commented on HADOOP-1300:
--------------------------------------

> > is there any reasons to adopt different policies for allocation and deletion?
> For allocation, where to place a replica has an effect on performance. But for deletion, the cost of deleting any replica is the same.

I meant when replication is set to 4 or higher, are we "maximizing the number of unique racks" for the rest of the blocks?

Talking with Hairong, now I understand that we don't do this in allocation/replication to simplify the code.
Thanks! 

> deletion of excess replicas does not take into account 'rack-locality'
> ----------------------------------------------------------------------
>
>                 Key: HADOOP-1300
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1300
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>            Reporter: Koji Noguchi
>            Assignee: Hairong Kuang
>         Attachments: excessDel.patch
>
>
> One rack went down today, resulting in one missing block/file.
> Looking at the log, this block was originally over-replicated. 
> 3 replicas on one rack and 1 replica on another.
> Namenode decided to delete the latter, leaving 3 replicas on the same rack.
> It'll be nice if the deletion is also rack-aware.

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