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https://issues.apache.org/jira/browse/HDFS-5526?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13828224#comment-13828224
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Tsz Wo (Nicholas), SZE commented on HDFS-5526:
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If I understand the patch correctly, it regenerates the ./current/VERSION file
by first reading it from the storage and then overwrite layoutVersion. If a
new field is added to the ./current/VERSION file in a future release (e.g.
HDFS-2832 adds DatanodeUuid), then rollback will preserve it in the VERSION
file.
> Datanode cannot roll back to previous layout version
> ----------------------------------------------------
>
> Key: HDFS-5526
> URL: https://issues.apache.org/jira/browse/HDFS-5526
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Kihwal Lee
> Priority: Blocker
> Attachments: HDFS-5526.patch, HDFS-5526.patch
>
>
> Current trunk layout version is -48.
> Hadoop v2.2.0 layout version is -47.
> If a cluster is upgraded from v2.2.0 (-47) to trunk (-48), the datanodes
> cannot start with -rollback. It will fail with IncorrectVersionException.
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