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Date: Fri, 27 May 2011 10:14:48 +0000 (UTC)
From: "ramkrishna.s.vasudevan (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-107) Data-nodes should be formatted when
 the name-node is formatted.
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    [ https://issues.apache.org/jira/browse/HDFS-107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13040164#comment-13040164 ] 

ramkrishna.s.vasudevan commented on HDFS-107:
---------------------------------------------

Can we provide a config parameter saying 
'datanode.format.required'
If this value is set to true, whenever the DN starts we can update the DN namespace id 
with the NN namespace id.

If the value is set to false then we can continue with the existing behvaiour.

Kindly provide your comments.

> Data-nodes should be formatted when the name-node is formatted.
> ---------------------------------------------------------------
>
>                 Key: HDFS-107
>                 URL: https://issues.apache.org/jira/browse/HDFS-107
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Konstantin Shvachko
>
> The upgrade feature HADOOP-702 requires data-nodes to store persistently the namespaceID 
> in their version files and verify during startup that it matches the one stored on the name-node.
> When the name-node reformats it generates a new namespaceID.
> Now if the cluster starts with the reformatted name-node, and not reformatted data-nodes
> the data-nodes will fail with
> java.io.IOException: Incompatible namespaceIDs ...
> Data-nodes should be reformatted whenever the name-node is. I see 2 approaches here:
> 1) In order to reformat the cluster we call "start-dfs -format" or make a special script "format-dfs".
> This would format the cluster components all together. The question is whether it should start
> the cluster after formatting?
> 2) Format the name-node only. When data-nodes connect to the name-node it will tell them to
> format their storage directories if it sees that the namespace is empty and its cTime=0.
> The drawback of this approach is that we can loose blocks of a data-node from another cluster
> if it connects by mistake to the empty name-node.

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