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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-10419) Building HDFS on top of new storage layer (HDSL)
Date Sun, 18 Mar 2018 20:50:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-10419?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16404179#comment-16404179

Konstantin Shvachko commented on HDFS-10419:

I was thinking if we could come up with a more descriptive name than HDSL Will start with
two proposals:
# HDDS - Hadoop Dynamically Distributed Storage
# HDSS - Hadoop Dynamically Scaling Storage

> 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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