Jitendra Nath Pandey commented on HDFS-10419:

{quote}I thought that a better approach would be to let NameNode handle only 
the Path-to-INode mapping and move the rest to Ozone.
[~shv], this is a great idea, and will certainly work. I like the clean 
separation of responsibilities between Namenode that manages hierarchical paths 
and delegation of flat inode-id namespace to ozone. Since we don't re-use 
inode-ids this will be a lot simpler key space, with no requirement for 
versioning, or rename. We can either use ozone's KSM directly where inode-ids 
are keys in a default volume/bucket, or we can tweak KSM's implementation for a 
dedicated 'inode map'. 

Replicated KSM is in our immediate roadmap using RAFT (Apache Ratis) for 

> Building HDFS on top of new storage layer (HDSL)
> ------------------------------------------------
>                 Key: HDFS-10419
>                 URL: https://issues.apache.org/jira/browse/HDFS-10419
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>            Reporter: Jing Zhao
>            Assignee: Jing Zhao
>            Priority: Major
>         Attachments: Evolving NN using new block-container layer.pdf
> In HDFS-7240, Ozone defines storage containers to store both the data and the 
> metadata. The storage container layer provides an object storage interface 
> and aims to manage data/metadata in a distributed manner. More details about 
> storage containers can be found in the design doc in HDFS-7240.
> HDFS can adopt the storage containers to store and manage blocks. The general 
> idea is:
> # Each block can be treated as an object and the block ID is the object's key.
> # Blocks will still be stored in DataNodes but as objects in storage 
> containers.
> # The block management work can be separated out of the NameNode and will be 
> handled by the storage container layer in a more distributed way. The 
> NameNode will only manage the namespace (i.e., files and directories).
> # For each file, the NameNode only needs to record a list of block IDs which 
> are used as keys to obtain real data from storage containers.
> # A new DFSClient implementation talks to both NameNode and the storage 
> container layer to read/write.
> HDFS, especially the NameNode, can get much better scalability from this 
> design. Currently the NameNode's heaviest workload comes from the block 
> management, which includes maintaining the block-DataNode mapping, receiving 
> full/incremental block reports, tracking block states (under/over/miss 
> replicated), and joining every writing pipeline protocol to guarantee the 
> data consistency. These work bring high memory footprint and make NameNode 
> suffer from GC. HDFS-5477 already proposes to convert BlockManager as a 
> service. If we can build HDFS on top of the storage container layer, we not 
> only separate out the BlockManager from the NameNode, but also replace it 
> with a new distributed management scheme.
> The storage container work is currently in progress in HDFS-7240, and the 
> work proposed here is still in an experimental/exploring stage. We can do 
> this experiment in a feature branch so that people with interests can be 
> involved.
> A design doc will be uploaded later explaining more details.

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