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https://issues.apache.org/jira/browse/HDFS-7240?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16223735#comment-16223735
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Konstantin Shvachko commented on HDFS-7240:
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It is an interesting question whether Ozone should be a part of Hadoop. There
are two main reasons why I think it should not.
# With close to 500 sub-tasks, with 6 MB of code changes, and with a sizable
community behind, it looks to me like a whole new project.
It is essentially a new storage system, with different (than HDFS)
architecture, separate S3-like APIs. This is really great - the World sure
needs more distributed file systems. But it is not clear why Ozone should
co-exist with HDFS under the same roof.
# Ozone is probably just the first step in rebuilding HDFS under a new
architecture. With the next steps presumably being HDFS-10419 and HDFS-11118.
The design doc for the new architecture has never been published. I can only
assume based on some presentations and personal communications that the idea is
to use Ozone as a block storage, and re-implement NameNode, so that it stores
only a partial namesapce in memory, while the bulk of it (cold data) is
persisted to a local storage.
Such architecture makes me wonder if it solves Hadoop's main problems. There
are two main limitations in HDF
a) _The throughput of Namespace operations_. Which is limited by the number of
RPCs the NameNode can handle
b) _The number of objects_ (files + blocks) the system can maintain. Which is
limited by the memory size of the NameNode.
The RPC performance (a) is more important for Hadoop scalability than the
object count (b). The read RPCs being the main priority.
The new architecture targets the object count problem, but in the expense of
the RPC throughput. Which seems to be a wrong resolution of the tradeoff.
Also based on the use patterns on our large clusters we read up to 90% of the
data we write, so cold data is a small fraction and most of it must be cached.
To summarize:
- Ozone is a big enough system to deserve its own project.
- The architecture that Ozone leads to does not seem to solve the intrinsic
problems of current HDFS.
> Object store in HDFS
> --------------------
>
> Key: HDFS-7240
> URL: https://issues.apache.org/jira/browse/HDFS-7240
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Jitendra Nath Pandey
> Assignee: Jitendra Nath Pandey
> Attachments: HDFS-7240.001.patch, HDFS-7240.002.patch,
> HDFS-7240.003.patch, HDFS-7240.003.patch, HDFS-7240.004.patch,
> Ozone-architecture-v1.pdf, Ozonedesignupdate.pdf, ozone_user_v0.pdf
>
>
> This jira proposes to add object store capabilities into HDFS.
> As part of the federation work (HDFS-1052) we separated block storage as a
> generic storage layer. Using the Block Pool abstraction, new kinds of
> namespaces can be built on top of the storage layer i.e. datanodes.
> In this jira I will explore building an object store using the datanode
> storage, but independent of namespace metadata.
> I will soon update with a detailed design document.
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