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https://issues.apache.org/jira/browse/HDFS-5448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13813734#comment-13813734
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Konstantin Shvachko commented on HDFS-5448:
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Ah yes, this is a legacy and pretty confusing part of code, which remained from
the times when DNs could not generate their own storageIDs. Now that they do,
see {{DataStorage.createStorageID()}}, this code path is just never triggered,
because nodeReg.getStorageID() is never empty.
So in practice NameNode never generates storageIDs for DNs.
> Datanode should generate its ID on first registration
> -----------------------------------------------------
>
> Key: HDFS-5448
> URL: https://issues.apache.org/jira/browse/HDFS-5448
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: datanode
> Affects Versions: Heterogeneous Storage (HDFS-2832)
> Reporter: Arpit Agarwal
> Assignee: Arpit Agarwal
> Fix For: Heterogeneous Storage (HDFS-2832)
>
> Attachments: h5448.01.patch, h5448.03.patch, h5448.04.addendum.patch,
> h5448.04.patch
>
>
> Prior to the heterogeneous storage feature, each Datanode had a single
> storage ID which was generated by the Namenode on first registration. The
> storage ID used fixed Datanode identifiers like IP address and port, so that
> in a federated cluster, for example, all NameNodes would generate the same
> storage ID.
> With Heterogeneous storage, we have replaced the storage ID with a
> per-datanode identifier called the Datanode-UUID. The Datanode UUID is also
> assigned by a NameNode on first registration. In a federated cluster with
> multiple namenodes, there are two ways to ensure a unique Datanode UUID
> allocation:
> # Synchronize initial registration requests from the BPServiceActors. If a
> Datanode UUID is already assigned we don't need to synchronize.
> # The datanode assigns itself a UUID on initialization.
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