*Hi Jitendra and all,Thanks for putting this together. I caught up on the
discussion on JIRA and document at HDFS-10419, and still have the same
concerns raised earlier
about merging the Ozone branch to trunk.To recap these questions/concerns
at a very high level:* Wouldn't Ozone benefit from being a separate
project?* Why should it be merged now?I still believe that both Ozone and
Hadoop would benefit from Ozone being a separate project, and that there is
no pressing reason to merge Ozone/HDSL now.The primary reason I've heard
for merging is that the Ozone is that it's at a stage where it's ready for
user feedback. Second, that it needs to be merged to start on the NN
refactoring for HDFS-on-HDSL.First, without HDFS-on-HDSL support, users are
testing against the Ozone object storage interface. Ozone and HDSL
themselves are implemented as separate masters and new functionality bolted
onto the datanode. It also doesn't look like HDFS in terms of API or
featureset; yes, it speaks FileSystem, but so do many out-of-tree storage
systems like S3, Ceph, Swift, ADLS etc. Ozone/HDSL does not support popular
HDFS features like erasure coding, encryption, high-availability,
snapshots, hflush/hsync (and thus HBase), or APIs like WebHDFS or NFS. This
means that Ozone feels like a new, different system that could reasonably
be deployed and tested separately from HDFS. It's unlikely to replace many
of today's HDFS deployments, and from what I understand, Ozone was not
designed to do this.Second, the NameNode refactoring for HDFS-on-HDSL by
itself is a major undertaking. The discussion on HDFS-10419 is still
ongoing so it’s not clear what the ultimate refactoring will be, but I do
know that the earlier FSN/BM refactoring during 2.x was very painful
(introducing new bugs and making backports difficult) and probably should
have been deferred to a new major release instead. I think this refactoring
is important for the long-term maintainability of the NN and worth
pursuing, but as a Hadoop 4.0 item. Merging HDSL is also not a prerequisite
for starting this refactoring. Really, I see the refactoring as the
prerequisite for HDFS-on-HDSL to be possible.Finally, I earnestly believe
that Ozone/HDSL itself would benefit from being a separate project. Ozone
could release faster and iterate more quickly if it wasn't hampered by
Hadoop's release schedule and security and compatibility requirements.
There are also publicity and community benefits; it's an opportunity to
build a community focused on the novel capabilities and architectural
choices of Ozone/HDSL. There are examples of other projects that were
"incubated" on a branch in the Hadoop repo before being spun off to great
success.In conclusion, I'd like to see Ozone succeeding and thriving as a
separate project. Meanwhile, we can work on the HDFS refactoring required
to separate the FSN and BM and make it pluggable. At that point (likely in
the Hadoop 4 timeframe), we'll be ready to pursue HDFS-on-HDSL integration.*

On Mon, Feb 26, 2018 at 1:18 PM, Jitendra Pandey <jiten...@hortonworks.com>

>     Dear folks,
>            We would like to start a vote to merge HDFS-7240 branch into
> trunk. The context can be reviewed in the DISCUSSION thread, and in the
> jiras (See references below).
>     HDFS-7240 introduces Hadoop Distributed Storage Layer (HDSL), which is
> a distributed, replicated block layer.
>     The old HDFS namespace and NN can be connected to this new block layer
> as we have described in HDFS-10419.
>     We also introduce a key-value namespace called Ozone built on HDSL.
>     The code is in a separate module and is turned off by default. In a
> secure setup, HDSL and Ozone daemons cannot be started.
>     The detailed documentation is available at
>              https://cwiki.apache.org/confluence/display/HADOOP/
> Hadoop+Distributed+Storage+Layer+and+Applications
>     I will start with my vote.
>             +1 (binding)
>     Discussion Thread:
>               https://s.apache.org/7240-merge
>               https://s.apache.org/4sfU
>     Jiras:
>                https://issues.apache.org/jira/browse/HDFS-7240
>                https://issues.apache.org/jira/browse/HDFS-10419
>                https://issues.apache.org/jira/browse/HDFS-13074
>                https://issues.apache.org/jira/browse/HDFS-13180
>     Thanks
>     jitendra
>             On 2/13/18, 6:28 PM, "sanjay Radia" <sanjayo...@gmail.com>
> wrote:
>                 Sorry the formatting got messed by my email client.  Here
> it is again
>                 Dear
>                  Hadoop Community Members,
>                    We had multiple community discussions, a few meetings
> in smaller groups and also jira discussions with respect to this thread. We
> express our gratitude for participation and valuable comments.
>                 The key questions raised were following
>                 1) How the new block storage layer and OzoneFS benefit
> HDFS and we were asked to chalk out a roadmap towards the goal of a
> scalable namenode working with the new storage layer
>                 2) We were asked to provide a security design
>                 3)There were questions around stability given ozone brings
> in a large body of code.
>                 4) Why can’t they be separate projects forever or merged
> in when production ready?
>                 We have responded to all the above questions with detailed
> explanations and answers on the jira as well as in the discussions. We
> believe that should sufficiently address community’s concerns.
>                 Please see the summary below:
>                 1) The new code base benefits HDFS scaling and a roadmap
> has been provided.
>                 Summary:
>                   - New block storage layer addresses the scalability of
> the block layer. We have shown how existing NN can be connected to the new
> block layer and its benefits. We have shown 2 milestones, 1st milestone is
> much simpler than 2nd milestone while giving almost the same scaling
> benefits. Originally we had proposed simply milestone 2 and the community
> felt that removing the FSN/BM lock was was a fair amount of work and a
> simpler solution would be useful
>                   - We provide a new K-V namespace called Ozone FS with
> FileSystem/FileContext plugins to allow the users to use the new system.
> BTW Hive and Spark work very well on KV-namespaces on the cloud. This will
> facilitate stabilizing the new block layer.
>                   - The new block layer has a new netty based protocol
> engine in the Datanode which, when stabilized, can be used by  the old hdfs
> block layer. See details below on sharing of code.
>                 2) Stability impact on the existing HDFS code base and
> code separation. The new block layer and the OzoneFS are in modules that
> are separate from old HDFS code - currently there are no calls from HDFS
> into Ozone except for DN starting the new block  layer module if configured
> to do so. It does not add instability (the instability argument has been
> raised many times). Over time as we share code, we will ensure that the old
> HDFS continues to remains stable. (for example we plan to stabilize the new
> netty based protocol engine in the new block layer before sharing it with
> HDFS’s old block layer)
>                 3) In the short term and medium term, the new system and
> HDFS  will be used side-by-side by users. Side by-side usage in the short
> term for testing and side-by-side in the medium term for actual production
> use till the new system has feature parity with old HDFS. During this time,
> sharing the DN daemon and admin functions between the two systems is
> operationally important:
>                   - Sharing DN daemon to avoid additional operational
> daemon lifecycle management
>                   - Common decommissioning of the daemon and DN: One place
> to decommission for a node and its storage.
>                   - Replacing failed disks and internal balancing capacity
> across disks - this needs to be done for both the current HDFS blocks and
> the new block-layer blocks.
>                   - Balancer: we would like use the same balancer and
> provide a common way to balance and common management of the bandwidth used
> for balancing
>                   - Security configuration setup - reuse existing set up
> for DNs rather then a new one for an independent cluster.
>                 4) Need to easily share the block layer code between the
> two systems when used side-by-side. Areas where sharing code is desired
> over time:
>                   - Sharing new block layer’s  new netty based protocol
> engine for old HDFS DNs (a long time sore issue for HDFS block layer).
>                   - Shallow data copy from old system to new system is
> practical only if within same project and daemon otherwise have to deal
> with security setting and coordinations across daemons. Shallow copy is
> useful as customer migrate from old to new.
>                   - Shared disk scheduling in the future and in the short
> term have a single round robin rather than independent round robins.
>                 While sharing code across projects is technically possible
> (anything is possible in software),  it is significantly harder typically
> requiring  cleaner public apis etc. Sharing within a project though
> internal APIs is often simpler (such as the protocol engine that we want to
> share).
>                 5) Security design, including a threat model and and the
> solution has been posted.
>                 6) Temporary Separation and merge later: Several of the
> comments in the jira have argued that we temporarily separate the two code
> bases for now and then later merge them when the new code is stable:
>                   - If there is agreement to merge later, why bother
> separating now - there needs to be to be good reasons to separate now.  We
> have addressed the stability and separation of the new code from existing
> above.
>                   - Merge the new code back into HDFS later will be harder.
>                     **The code and goals will diverge further.
>                     ** We will be taking on extra work to split and then
> take extra work to merge.
>                     ** The issues raised today will be raised all the same
> then.
>                 ------------------------------
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