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
DISCUSSION THREAD SUMMARY :
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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