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https://issues.apache.org/jira/browse/HDFS-107?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13049234#comment-13049234
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Uma Maheswara Rao G commented on HDFS-107:
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I agree with you, But Removing complete storage directories will take good
amount of time when huge number of blocks present. Instead we can just sync the
namespeceIDs in DataNode startup based on the flag passed and let the blocks
will be deleted asynchronously.
> 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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