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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-692) Rack-aware Replica Placement
Date Thu, 09 Nov 2006 22:30:43 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-692?page=comments#action_12448601 ] 
            
Bryan Pendleton commented on HADOOP-692:
----------------------------------------

Seems implied here, but I'll state it anyway, just in case it should be a separate issue:

Reads should also be rack-aware. Requests to the NameNode can take the rack as an argument,
and order the returned locations by rack locality. This implies that there should be a mechanism
for a client to be told/discover what rack its on, too, so the argument to the datanode isn't
the only place rack information is useful.

> 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
>             Fix For: 0.9.0
>
>
> 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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