[jira] [Commented] (HDFS-10419) Building HDFS on top of Ozone's storage containers

["Konstantin Shvachko (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-10419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16336759#comment-16336759 ] 

Konstantin Shvachko commented on HDFS-10419:
--------------------------------------------

Read the document, but did not get enough information about the architecture for Milestones 1 and 2. [~sanjay.radia] it would be good to add more details on the changes to the NameNode, when blocks are maintained on Ozone. I can partially deduce the ideas behind Milestone 1, but Milestone 2 is not clear to me.
As a side note, I didn't understand why you used 50MB blocks in your math. The default is 128MB and many people run HDFS with 512MB blocks.

> Building HDFS on top of Ozone's storage containers
> --------------------------------------------------
>
>                 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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