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From Brian Bockelman <bbock...@cse.unl.edu>
Subject Re: Changing hostnames of tasktracker/datanode nodes - any problems?
Date Tue, 10 Aug 2010 14:07:25 GMT
Hi Erik,

You can also do this one-by-one (aka, a rolling reboot).  Shut it down, wait for it to be
recognized as dead, then bring it back up with a new hostname.  It will take a much longer
time, but you won't have any decrease in availability, just some minor decrease in capacity.

This is useful in sites like ours where we have 24/7 usage and try to avoid any unnecessary


On Aug 10, 2010, at 8:42 AM, Allen Wittenauer wrote:

> On Aug 10, 2010, at 3:51 AM, Erik Forsberg wrote:
>> Hi!
>> Due to network reconfigurations, I need to change the hostnames of some
>> of my worker nodes, i.e. the nodes running tasktracker and datanode. I
>> need to do this to make my hostname naming schema actually concur with
>> the network setup.
>> Are there any problems doing this? It seems HDFS identifies things
>> using some kind of hostname-independent UID, so I guess it should
>> recover from one machine going down and then appear again under another
>> hostname?
> The name node metadata only matches blocks #s to files.  The data node to block part
is determined at run time.  So it is perfectly safe and legal to:
> a) bring grid down
> b) rename everything
> c) fix config files
> d) bring grid up
> Don't forget to change your network topology script, slaves, and dfs.hosts as necessary.
 If fsck complains about topology violations, use setrep to increase then setrep to decrease
the violated files.

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