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From "Eric Sirianni (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-5454) DataNode UUID should be assigned prior to FsDataset initialization
Date Thu, 12 Dec 2013 21:35:07 GMT

    [ https://issues.apache.org/jira/browse/HDFS-5454?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13846763#comment-13846763
] 

Eric Sirianni commented on HDFS-5454:
-------------------------------------

+1 for the patch.  I've made a similar change internally and can confirm that it fixes the
issue we are seeing in our {{FsDatasetSpi}} plugin.

> DataNode UUID should be assigned prior to FsDataset initialization
> ------------------------------------------------------------------
>
>                 Key: HDFS-5454
>                 URL: https://issues.apache.org/jira/browse/HDFS-5454
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode
>    Affects Versions: 3.0.0
>            Reporter: Eric Sirianni
>            Priority: Minor
>         Attachments: HDFS-5454.01.patch
>
>
> The DataNode's UUID ({{DataStorage.getDatanodeUuid()}} field) is NULL at the point where
the {{FsDataset}} object is created ({{DataNode.initStorage()}}.  
> As the {{DataStorage}} object is an input to the {{FsDataset}} factory method, it is
desirable for it to be fully populated with a UUID at this point.  In particular, our {{FsDatasetSpi}}
implementation relies upon the DataNode UUID as a key to access our underlying block storage
device.
> This also appears to be a regression compared to Hadoop 1.x - our 1.x {{FSDatasetInterface}}
plugin has a non-NULL UUID on startup.  I haven't fully traced through the code, but I suspect
this came from the {{BPOfferService}}/{{BPServiceActor}} refactoring to support federated
namenodes.
> With HDFS-5448, the DataNode is now responsible for generating its own UUID.  This greatly
simplifies the fix.  Move the UUID check/generation in from {{DataNode.createBPRegistration()}}
to {{DataNode.initStorage()}}.  This more naturally co-locates UUID generation immediately
subsequent to the read of the UUID from the {{DataStorage}} properties file.
> {code}
>   private void initStorage(final NamespaceInfo nsInfo) throws IOException {
>     // ...
>       final String bpid = nsInfo.getBlockPoolID();
>       //read storage info, lock data dirs and transition fs state if necessary
>       storage.recoverTransitionRead(this, bpid, nsInfo, dataDirs, startOpt);
>       
>       // SUGGESTED NEW PLACE TO CHECK DATANODE UUID
>       checkDatanodeUuid();
>     // ...
>   }
> {code}



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