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From "Owen O'Malley" <o...@yahoo-inc.com>
Subject Re: dfs incompatibility .3 and .4-dev?
Date Wed, 07 Jun 2006 07:29:54 GMT
On Jun 6, 2006, at 7:36 AM, Stefan Groschupf wrote:

> Hi,
> we discussed the three  kinds of data looses, hardware, software or 
> human errors.
> I would love to figure out what was my problem today. :)
>
> Scenario:
> + updated from hadoop .2.1 to .4.
> + problems to get all datanodes started
> + downgrade to hadoop .3.1
> + error message of incompatible dfs (I guess . already had started to 
> write to the log)

Actually, you must have downgraded to pre-HADOOP-124. Since I just did 
that downgrade on one of my clusters, I figured out the format changes. 
(This is only for those of you who are stuck and feel very comfortable 
editing binary files in the editor of your choice. Please be careful 
and keep backups.)

For downgrading dfs namenodes from 0.3.* or 0.4-dev to 0.3-dev (svn rev 
<= 410634):

1. For <name-node-dir>/image/fsimage
   a. change byte 4 from fe to ff
   b. delete bytes 5 to 8

2. For <name-node-dir>/edits:
   a. change byte 4 from fe to ff

-- Owen


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