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From Suresh Srinivas <sur...@hortonworks.com>
Subject Re: HDFS / Federated HDFS - Doubts
Date Wed, 16 Oct 2013 17:48:40 GMT
On Wed, Oct 16, 2013 at 9:22 AM, Steve Edison <sedison70@gmail.com> wrote:

> I have couple of questions about HDFS federation:
> Can I state different block store directories for each namespace on a
> datanode ?

No. The main idea of federation was not to physically partition the storage
across namespace, but to use all the available storage across the
namespaces, to ensure better utilzation.

> Can I have some datanodes dedicated to a particular namespace only ?

As I said earlier, all the datanodes are shared across namespaces. If you
want to dedicate datanodes to a particular namespace, you might as well
create it as two separate clusters with different set of datanodes and a
separate namespace.

> This seems quite interesting. Way to go !
> On Tue, Oct 1, 2013 at 9:52 PM, Krishna Kumaar Natarajan <natar033@umn.edu
> > wrote:
>> Hi All,
>> While trying to understand federated HDFS in detail I had few doubts and
>> listing them down for your help.
>>    1. In case of *HDFS(without HDFS federation)*, the metadata or the
>>    data about the blocks belonging to the files in HDFS is maintained in the
>>    main memory of the name node or it is stored on permanent storage of the
>>    namenode and is brought in the main memory on demand basis ? [Krishna]
>>    Based on my understanding, I assume the entire metadata is in main memory
>>    which is an issue by itself. Please correct me if my understanding is wrong.
>>    2. In case of* federated HDFS*, the metadata or the data about the
>>    blocks belonging to files in a particular namespace is maintained in the
>>    main memory of the namenode or it is stored on the permanent storage of the
>>    namenode and is brought in the main memory on demand basis ?
>>    3. Are the metadata information stored in separate cluster
>>    nodes(block management layer separation) as discussed in Appendix B of this
>>    document ?
>>    https://issues.apache.org/jira/secure/attachment/12453067/high-level-design.pdf
>>    4. I would like to know if the following proposals are already
>>    implemented in federated HDFS. (
>>    http://www.slideshare.net/hortonworks/hdfs-futures-namenode-federation-for-improved-efficiency-and-scalability
>>     slide-17)
>>    - Separation of namespace and block management layers (same as qn.3)
>>       - Partial namespace in memory for further scalability
>>       - Move partial namespace from one namenode to another
>> Thanks,
>> Krishna


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