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https://issues.apache.org/jira/browse/HDFS-8286?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14623205#comment-14623205
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Yong Zhang commented on HDFS-8286:
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If HDFS keep metadata in a persistent KV store, such as leveldb, is fsimage 
necessary?

> Scaling out the namespace using KV store
> ----------------------------------------
>
>                 Key: HDFS-8286
>                 URL: https://issues.apache.org/jira/browse/HDFS-8286
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Haohui Mai
>            Assignee: Haohui Mai
>         Attachments: hdfs-kv-design.pdf
>
>
> Currently the NN keeps the namespace in the memory. To improve the 
> scalability of the namespace, users can scale up by using more RAM or scale 
> out using Federation (i.e., statically partitioning the namespace).
> We would like to remove the limitation of scaling the global namespace. Our 
> vision is that that HDFS should adopt a scalable underlying architecture that 
> allows the global namespace scales linearly.
> We propose to implement the HDFS namespace on top of a key-value (KV) store. 
> Adopting the KV store interfaces allows HDFS to leverage the capability of 
> modern KV store and to become much easier to scale. Going forward, the 
> architecture allows distributing the namespace across multiple machines, or  
> storing only the working set in the memory (HDFS-5389), both of which allows  
> HDFS to manage billions of files using the commodity hardware available today.



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