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https://issues.apache.org/jira/browse/HDFS-11464?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15904232#comment-15904232
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Chris Douglas commented on HDFS-11464:
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bq. the storage chosen by the NameNode doesn't matter as the DataNode picks
target volumes (via VolumeChoosingPolicy)
The storage chosen by the NameNode could be included and passed to the DataNode
(HDFS-9807). We need to pass this information for tiered storage, but it could
also be used for centralized policies.
> Improve the selection in choosing storage for blocks
> ----------------------------------------------------
>
> Key: HDFS-11464
> URL: https://issues.apache.org/jira/browse/HDFS-11464
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Reporter: Yiqun Lin
> Assignee: Yiqun Lin
> Attachments: HDFS-11464.001.patch
>
>
> Currently the logic in choosing storage for blocks is not a good way. It
> always uses the first valid storage of a given StorageType ({{see
> DataNodeDescriptor#chooseStorage4Block}}). This should not be a good
> selection. That means blcoks will always be written to the same volume (first
> volume) and other valid volumes have no choices. This problem is brought up
> by this comment (
> https://issues.apache.org/jira/browse/HDFS-9807?focusedCommentId=15878382&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-15878382
> )
> There is one solution from me:
> * First, based on existing storages in one node, extract all the valid
> storages into a collection.
> * Then, disrupt the order of these vaild storages, get a new collection.
> * Finally, get the first storage from the new storages collection.
> These steps will be executed in {{DataNodeDescriptor#chooseStorage4Block}}
> and replace current logic. I think this improvement can be done as a subtask
> under HDFS-11419. Any further comments are welcomed.
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