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https://issues.apache.org/jira/browse/HDFS-5754?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13878500#comment-13878500
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Tsz Wo (Nicholas), SZE commented on HDFS-5754:
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In the new patch, LayoutVersion.Feature is still moved to NameNode. We should
only move ROLLING_UPGRADE_MARKER to NameNode and keep the other features such
as ADD_DATANODE_AND_STORAGE_UUIDS in LayoutVersion. Obviously,
ADD_DATANODE_AND_STORAGE_UUIDS is not a namenode feature. Indeed, all the
pre-rolling upgrade features (i.e. lv-1 - lv-51) are shared by NN and DN. We
cannot move them to NN.
> Split LayoutVerion into NamenodeLayoutVersion and DatanodeLayoutVersion
> ------------------------------------------------------------------------
>
> Key: HDFS-5754
> URL: https://issues.apache.org/jira/browse/HDFS-5754
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode, namenode
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Brandon Li
> Attachments: HDFS-5754.001.patch, HDFS-5754.002.patch,
> HDFS-5754.003.patch, HDFS-5754.004.patch, HDFS-5754.006.patch
>
>
> Currently, LayoutVersion defines the on-disk data format and supported
> features of the entire cluster including NN and DNs. LayoutVersion is
> persisted in both NN and DNs. When a NN/DN starts up, it checks its
> supported LayoutVersion against the on-disk LayoutVersion. Also, a DN with a
> different LayoutVersion than NN cannot register with the NN.
> We propose to split LayoutVersion into two independent values that are local
> to the nodes:
> - NamenodeLayoutVersion - defines the on-disk data format in NN, including
> the format of FSImage, editlog and the directory structure.
> - DatanodeLayoutVersion - defines the on-disk data format in DN, including
> the format of block data file, metadata file, block pool layout, and the
> directory structure.
> The LayoutVersion check will be removed in DN registration. If
> NamenodeLayoutVersion or DatanodeLayoutVersion is changed in a rolling
> upgrade, then only rollback is supported and downgrade is not.
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