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https://issues.apache.org/jira/browse/HDFS-5448?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13811680#comment-13811680
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Arpit Agarwal commented on HDFS-5448:
-------------------------------------
No drawback, unless we want to let NameNodes manage the UUID assignment.
{quote}
An issue with relying on the NameNode handshake to assign the UUID is that
there is a lengthy period during DataNode initialization where the DatanodeUuid
is still NULL. In particular, when the FsDatasetSpi is created in
initStorage(), the DatanodeUuid is NULL. The DatanodeUuid is not set afterwards
until bpRegistrationSucceeded().
{quote}
[~sirianni], I believe this is not very different from today where the
storageID remains unassigned until after the first handshake.
> Synchronize NN registrations across BPServiceActors
> ---------------------------------------------------
>
> 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
> Attachments: h5448.01.patch, h5448.03.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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