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Date: Mon, 13 Jun 2011 22:55:47 +0000 (UTC)
From: "Todd Lipcon (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=13048852#comment-13048852 ] 

Todd Lipcon commented on HDFS-107:
----------------------------------

I think adding another config here is unnecessary. What's the downside of adding a "-format" flag to the datanode, and having "start-dfs -format" pass it along?

> 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
>    Affects Versions: 0.23.0
>            Reporter: Konstantin Shvachko
>         Attachments: HDFS-107-1.patch
>
>
> 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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