[jira] Commented: (HADOOP-1212) Data-nodes should be formatted when the name-node is formatted.

["Stu Hood (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-1212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12515391 ] 

Stu Hood commented on HADOOP-1212:
----------------------------------

Does anyone have any thoughts on this issue? I've been getting "Incompatible namespaceID" errors on my datanodes after formatting with `bin/hadoop namenode -format`. My current solution is to remove the hadoop-*-data directory on each datanode, but there ought to be a better way.

Thanks.

> Data-nodes should be formatted when the name-node is formatted.
> ---------------------------------------------------------------
>
>                 Key: HADOOP-1212
>                 URL: https://issues.apache.org/jira/browse/HADOOP-1212
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.12.2
>            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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