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From Konstantin Shvachko <shv.had...@gmail.com>
Subject Re: [DISCUSSION] Merging HDFS-7240 Object Store (Ozone) to trunk
Date Sat, 28 Oct 2017 21:00:52 GMT
Hey guys,

It is an interesting question whether Ozone should be a part of Hadoop.
There are two main reasons why I think it should not.

1. 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.

2. 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 HDFS:
  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.

I will post my opinion in the Ozone jira. Should be more convenient to
discuss it there for further reference.

Thanks,
--Konstantin



On Wed, Oct 18, 2017 at 6:54 PM, Yang Weiwei <cheersyang@hotmail.com> wrote:

> Hello everyone,
>
>
> I would like to start this thread to discuss merging Ozone (HDFS-7240) to
> trunk. This feature implements an object store which can co-exist with
> HDFS. Ozone is disabled by default. We have tested Ozone with cluster sizes
> varying from 1 to 100 data nodes.
>
>
>
> The merge payload includes the following:
>
>   1.  All services, management scripts
>   2.  Object store APIs, exposed via both REST and RPC
>   3.  Master service UIs, command line interfaces
>   4.  Pluggable pipeline Integration
>   5.  Ozone File System (Hadoop compatible file system implementation,
> passes all FileSystem contract tests)
>   6.  Corona - a load generator for Ozone.
>   7.  Essential documentation added to Hadoop site.
>   8.  Version specific Ozone Documentation, accessible via service UI.
>   9.  Docker support for ozone, which enables faster development cycles.
>
>
> To build Ozone and run ozone using docker, please follow instructions in
> this wiki page. https://cwiki.apache.org/confl
> uence/display/HADOOP/Dev+cluster+with+docker.
>
>
> We have built a passionate and diverse community to drive this feature
> development. As a team, we have achieved significant progress in past 3
> years since first JIRA for HDFS-7240 was opened on Oct 2014. So far, we
> have resolved almost 400 JIRAs by 20+ contributors/committers from
> different countries and affiliations. We also want to thank the large
> number of community members who were supportive of our efforts and
> contributed ideas and participated in the design of ozone.
>
>
> Please share your thoughts, thanks!
>
>
> -- Weiwei Yang
>


On Wed, Oct 18, 2017 at 6:54 PM, Yang Weiwei <cheersyang@hotmail.com> wrote:

> Hello everyone,
>
>
> I would like to start this thread to discuss merging Ozone (HDFS-7240) to
> trunk. This feature implements an object store which can co-exist with
> HDFS. Ozone is disabled by default. We have tested Ozone with cluster sizes
> varying from 1 to 100 data nodes.
>
>
>
> The merge payload includes the following:
>
>   1.  All services, management scripts
>   2.  Object store APIs, exposed via both REST and RPC
>   3.  Master service UIs, command line interfaces
>   4.  Pluggable pipeline Integration
>   5.  Ozone File System (Hadoop compatible file system implementation,
> passes all FileSystem contract tests)
>   6.  Corona - a load generator for Ozone.
>   7.  Essential documentation added to Hadoop site.
>   8.  Version specific Ozone Documentation, accessible via service UI.
>   9.  Docker support for ozone, which enables faster development cycles.
>
>
> To build Ozone and run ozone using docker, please follow instructions in
> this wiki page. https://cwiki.apache.org/confluence/display/HADOOP/Dev+
> cluster+with+docker.
>
>
> We have built a passionate and diverse community to drive this feature
> development. As a team, we have achieved significant progress in past 3
> years since first JIRA for HDFS-7240 was opened on Oct 2014. So far, we
> have resolved almost 400 JIRAs by 20+ contributors/committers from
> different countries and affiliations. We also want to thank the large
> number of community members who were supportive of our efforts and
> contributed ideas and participated in the design of ozone.
>
>
> Please share your thoughts, thanks!
>
>
> -- Weiwei Yang
>

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