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From Ascot Moss <ascot.m...@gmail.com>
Subject Re: HDFS2 vs MaprFS
Date Mon, 06 Jun 2016 15:26:39 GMT
I don't think HDFS2 needs SAN, use the QuorumJournal approach is much
better than using Shared edits directory SAN approach.



On Monday, June 6, 2016, Peyman Mohajerian <mohajeri@gmail.com> wrote:

> It is very common practice to backup the metadata in some SAN store. So
> the idea of complete loss of all the metadata is preventable. You could
> lose a day worth of data if e.g. you back the metadata once a day but you
> could do it more frequently. I'm not saying S3 or Azure Blob are bad ideas.
>
> On Sun, Jun 5, 2016 at 8:19 AM, Marcin Tustin <mtustin@handybook.com>
> wrote:
>
>> The namenode architecture is a source of fragility in HDFS. While a high
>> availability deployment (with two namenodes, and a failover mechanism)
>> means you're unlikely to see service interruption, it is still possible to
>> have a complete loss of filesystem metadata with the loss of two machines.
>>
>> Secondly, because HDFS identifies datanodes by their hostname/ip, dns
>> changes can cause havoc with HDFS (see my war story on this here:
>> https://medium.com/handy-tech/renaming-hdfs-datanodes-considered-terribly-harmful-2bc2f37aabab
>> ).
>>
>> Also, the namenode/datanode architecture probably does contribute to the
>> small files problem being a problem. That said, there are lot of practical
>> solutions for the small files problem.
>>
>> If you're just setting up a data infrastructure, I would say consider
>> alternatives before you pick HDFS. If you run in AWS, S3 is a good
>> alternative. If you run in some other cloud, it's probably worth
>> considering whatever their equivalent storage system is.
>>
>>
>> On Sat, Jun 4, 2016 at 7:43 AM, Ascot Moss <ascot.moss@gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I read some (old?) articles from Internet about Mapr-FS vs HDFS.
>>>
>>> https://www.mapr.com/products/m5-features/no-namenode-architecture
>>>
>>> It states that HDFS Federation has
>>>
>>> a) "Multiple Single Points of Failure", is it really true?
>>> Why MapR uses HDFS but not HDFS2 in its comparison as this would lead to
>>> an unfair comparison (or even misleading comparison)?  (HDFS was from
>>> Hadoop 1.x, the old generation) HDFS2 is available since 2013-10-15, there
>>> is no any Single Points of  Failure in HDFS2.
>>>
>>> b) "Limit to 50-200 million files", is it really true?
>>> I have seen so many real world Hadoop Clusters with over 10PB data, some
>>> even with 150PB data.  If "Limit to 50 -200 millions files" were true in
>>> HDFS2, why are there so many production Hadoop clusters in real world? how
>>> can they mange well the issue of  "Limit to 50-200 million files"? For
>>> instances,  the Facebook's "Like" implementation runs on HBase at Web
>>> Scale, I can image HBase generates huge number of files in Facbook's Hadoop
>>> cluster, the number of files in Facebook's Hadoop cluster should be much
>>> much bigger than 50-200 million.
>>>
>>> From my point of view, in contrast, MaprFS should have true limitation
>>> up to 1T files while HDFS2 can handle true unlimited files, please do
>>> correct me if I am wrong.
>>>
>>> c) "Performance Bottleneck", again, is it really true?
>>> MaprFS does not have namenode in order to gain file system performance.
>>> If without Namenode, MaprFS would lose Data Locality which is one of the
>>> beauties of Hadoop  If Data Locality is no longer available, any big data
>>> application running on MaprFS might gain some file system performance but
>>> it would totally lose the true gain of performance from Data Locality
>>> provided by Hadoop's namenode (gain small lose big)
>>>
>>> d) "Commercial NAS required"
>>> Is there any wiki/blog/discussion about Commercial NAS on Hadoop
>>> Federation?
>>>
>>> regards
>>>
>>>
>>>
>>>
>>
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>

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