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https://issues.apache.org/jira/browse/HDFS-107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12985402#action_12985402
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Konstantin Shvachko commented on HDFS-107:
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In the current scenario data-nodes cannot mistakenly connect to another
name-node as they will have different namespaceIds, and therefore blocks cannot
be invalidated. Approach (2) will break this, but only in case of cTime=0.
> 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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