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From Stanley Shi <s...@gopivotal.com>
Subject Re: Rack awareness and pipeline write
Date Mon, 12 May 2014 02:36:24 GMT
in some case you may not find the third node to place replica.

*Stanley Shi,*

On Sun, May 11, 2014 at 10:55 AM, jianan hu <hujianan@gmail.com> wrote:

> Hi everyone,
> See HDFS documents, It says "For the common case, when the replication
> factor is three, HDFS’s placement policy is to put one replica on one node
> in the local rack, another on a node in a different (remote) rack, and the
> last on a different node in the same remote rack."
> Assume there are two racks A and B. According to rack awareness, the first
> block is put in rack A, and the the other two replicated blocks will be
> pushed into rack B.
> However, why not store the first and second replicas in the local rack
> (A), and the last in a different remote rack (B)? Both two scenarios have
> same network traffic. What's the disadvantage of it?
> Thanks.
> Best Regards,
> Jianan

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