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From "Runping Qi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-692) Rack-aware Replica Placement
Date Tue, 05 Dec 2006 23:32:22 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-692?page=comments#action_12455794 ] 
            
Runping Qi commented on HADOOP-692:
-----------------------------------


When re-replicating, we should try to place replicas to different racks whenever it is feasible.

To minimize write latency, when we write a block that needs more than 2 replicas, does it
make sense to let the client return after writing the first 2 copies onto dofferent racks,
and let the background re-plication process take care the other replicas?

 

> Rack-aware Replica Placement
> ----------------------------
>
>                 Key: HADOOP-692
>                 URL: http://issues.apache.org/jira/browse/HADOOP-692
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.8.0
>            Reporter: Hairong Kuang
>         Assigned To: Hairong Kuang
>         Attachments: Rack_aware_HDFS_proposal.pdf
>
>
> This issue assumes that HDFS runs on a cluster of computers that spread across many racks.
Communication between two nodes on different racks needs to go through switches. Bandwidth
in/out of a rack may be less than the total bandwidth of machines in the rack. The purpose
of rack-aware replica placement is to improve data reliability, availability, and network
bandwidth utilization. The basic idea is that each data node determines to which rack it belongs
at the startup time and notifies the name node of the rack id upon registration. The name
node maintains a rackid-to-datanode map and tries to place replicas across racks.

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