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From Peyman Mohajerian <mohaj...@gmail.com>
Subject Re: HDFS2 vs MaprFS
Date Sun, 05 Jun 2016 19:14:04 GMT
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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