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From "Owen O'Malley" <owen.omal...@gmail.com>
Subject Re: [VOTE] Merging branch HDFS-7240 to trunk
Date Fri, 02 Mar 2018 00:05:17 GMT
I think it would be good to get this in sooner rather than later, but I
have some thoughts.

   1. It is hard to tell what has changed. git rebase -i tells me the
   branch has 722 commits. The rebase failed with a conflict. It would really
   help if you rebased to current trunk.
   2. I think Ozone would be a good Hadoop subproject, but it should be
   outside of HDFS.
   3. CBlock, which is also coming in this merge, would benefit from more
   separation from HDFS.
   4. What are the new transitive dependencies that Ozone, HDSL, and CBlock
   adding to the clients? The servers matter too, but the client dependencies
   have a huge impact on our users.
   5. Have you checked the new dependencies for compatibility with ASL?

On Thu, Mar 1, 2018 at 2:45 PM, Clay B. <cwb@clayb.net> wrote:

> Oops, retrying now subscribed to more than solely yarn-dev.
> -Clay
> On Wed, 28 Feb 2018, Clay B. wrote:
> +1 (non-binding)
>> I have walked through the code and find it very compelling as a user; I
>> really look forward to seeing the Ozone code mature and it maturing HDFS
>> features together. The points which excite me as an eight year HDFS user
>> are:
>> * Excitement for making the datanode a storage technology container - this
>>  patch clearly brings fresh thought to HDFS keeping it from growing stale
>> * Ability to build upon a shared storage infrastructure for diverse
>>  loads: I do not want to have "stranded" storage capacity or have to
>>  manage competing storage systems on the same disks (and further I want
>>  the metrics datanodes can provide me today, so I do not have to
>>  instrument two systems or evolve their instrumentation separately).
>> * Looking forward to supporting object-sized files!
>> * Moves HDFS in the right direction to test out new block management
>>  techniques for scaling HDFS. I am really excited to see the raft
>>  integration; I hope it opens a new era in Hadoop matching modern systems
>>  design with new consistency and replication options in our ever
>>  distributed ecosystem.
>> -Clay
>> On Mon, 26 Feb 2018, Jitendra Pandey wrote:
>>    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" <sanjayosrc@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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