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https://issues.apache.org/jira/browse/HADOOP-993?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12481712
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dhruba borthakur commented on HADOOP-993:
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I would say that the the motivation behind this is to make the architecture
cleaner and simple. The filesystem image need not store cluster configuration
(i.e. datanodes). Regarding you points:
* "in case of a misconfiguration of a datanode, namenode can tell which
datanode "should" have a certain storageid" -- You might be right here. But
from my understanding, we have never had exploited this particular feature on
our kryptonite cluster till now.
* "lastly - UI can report on missing datanodes, which proved immensely useful
for administration" -- The preferred method to maintain cluster membership info
is in the include/exclude files. The include/exclude file support was
introduced recently.
I think it is architecturally sound to keep cluster membership info separate
from filesystem namespace information. It might help in clustering the namenode
(thru namespace partitioning) or in namenode failover scenarios in the future.
I agree with you that the cluster administrator will not be able to see dead
data nodes in the UI anymore. This seems to be the biggest drawback of this
patch. If the adminstrator wants to view all datanodes in the UI, he/she has to
create a include file (manually) and list all datanodes in that file. Do you
agree that this alternative is acceptable?
> Namenode does not need to store any data node info persistently.
> ----------------------------------------------------------------
>
> Key: HADOOP-993
> URL: https://issues.apache.org/jira/browse/HADOOP-993
> Project: Hadoop
> Issue Type: Improvement
> Components: dfs
> Reporter: Raghu Angadi
> Assigned To: Sameer Paranjpye
> Attachments: noDatanodesInFsimage.patch
>
>
> Namenode does not need to serialize datanode info. It will map datanode to
> storageID when datanode register.
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