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From "lohit vijayarenu (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-2559) DFS should place one replica per rack
Date Wed, 05 Mar 2008 11:03:40 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-2559?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

lohit vijayarenu updated HADOOP-2559:
-------------------------------------

    Attachment: Trunk_Rack_Node_Mapping.jpg

Node alloation across Racks while running against Trunk

> DFS should place one replica per rack
> -------------------------------------
>
>                 Key: HADOOP-2559
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2559
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: Runping Qi
>            Assignee: lohit vijayarenu
>         Attachments: HADOOP-2559-1.patch, HADOOP-2559-2.patch, Patch1_Block_Report.png.jpg,
Patch1_Rack_Node_Mapping.jpg, Patch2 Block Report.jpg, Trunk_Block_Report.png, Trunk_Rack_Node_Mapping.jpg
>
>
> Currently, when writing out a block, dfs will place one copy to a local data node, one
copy to a rack local node
> and another one to a remote node. This leads to a number of undesired properties:
> 1. The block will be rack-local to two tacks instead of three, reducing the advantage
of rack locality based scheduling by 1/3.
> 2. The Blocks of a file (especiallya  large file) are unevenly distributed over the nodes:
One third will be on the local node, and two thirds on the nodes on the same rack. This may
make some nodes full much faster than others, 
> increasing the need of rebalancing. Furthermore, this also make some nodes become "hot
spots" if those big 
> files are popular and accessed by many applications.

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