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From Raghu Angadi <rang...@yahoo-inc.com>
Subject Re: Question on relocation of Hadoop cluster
Date Thu, 04 Oct 2007 03:49:59 GMT
Taeho Kang wrote:
> Hello all.
> Due to limited space in current datacenter, I am trying to move my Hadoop
> cluster to a new datacenter.
> In the new datacenter, each machine will keep its hostname, but each will be
> assigned to a new ip address.
> We should be able to edit our DNS to assign existing hostnames to new ip
> addresses.
> My understanding is that namenode keeps track of a datanode with an ip
> address, not a hostname.
> (According to the description found on for "private String hostName" in
> DatanodeInfo.java class)

Namenode keeps track of these just as convenience for the admins. In 
fact in trunk it does not store any datanode info. So its ok even if 
both hostnames and ipaddress change. Only side effect is that if the 
ipaddresses change you will all the old ip listed under 'dead nodes' on 
webui (which will go away when you upgrade to 0.15.x).

> Thus, the datanode / block info will be obsolete if the Hadoop cluster is
> moved unless we do modify all the datanode / block info in the namenode....

I don't think so.

> The solutions that I can think of right now is...

Could you state the problem again? Essentially you have to move the data 
to new datacenter.


> 1. modify all the datanode / block info : quite a risky work, i guess.
> 2. Have some "buffer" servers and have the data moved to there, and then to
> the moved cluster in the new datacenter : but then it would require some
> machines with lots of free storage and very careful planning.
> Any comments on my solutions or any other suggestions will be welcomed!
> Thank you all in advance.
> Regards,
> Taeho
> p.s. Any future plan to hava the datanode info with a hostname instead of an
> ip address?
> Also, what was the motivation behind using an ipaddress instead of a
> hostname to identify datanodes?

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