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From: Preethi Vinayak Ponangi <vinayakponangi@gmail.com>
Date: Sat, 26 Jan 2013 10:46:58 -0600
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 <CAMsUEeSpiw6ONqy7DxDENaChaoP6jTNEYbuKfEwzGMLjX+qtbg@mail.gmail.com>
Subject: Re: Difference between HDFS and local filesystem
To: user@hadoop.apache.org
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Yes. It's possible to use your local file system instead of HDFS. As you
said, doesn't really matter when you are running a pseudo-distributed
cluster. This is generally fine if your dataset is fairly small. The place
where HDFS access really shines is if your file is huge, generally several
TB or PB. That is when individual mappers can access different partitioned
data on different nodes improving performance.

In a fully distributed mode, your data gets partitioned and gets stored on
several different nodes on HDFS.
But when you use local data, the data is not replication or partitioned,
it's just like accessing a single file.

On Sat, Jan 26, 2013 at 9:49 AM, Sundeep Kambhampati <
kambhamp@cse.ohio-state.edu> wrote:

> Hi Users,
> I am kind of new to MapReduce programming I am trying to understand the
> integration between MapReduce and HDFS.
> I could understand MapReduce can use HDFS for data access. But is possible
> not to use HDFS at all and run MapReduce programs?
> HDFS does file replication and partitioning. But if I use the following
> command to run the Example MaxTemperature
>
>  bin/hadoop jar /usr/local/hadoop/maxtemp.jar MaxTemperature
> file:///usr/local/ncdcinput/**sample.txt file:///usr/local/out4
>
> instead of
>
>  bin/hadoop jar /usr/local/hadoop/maxtemp.jar MaxTemperature
> usr/local/ncdcinput/sample.txt usr/local/out4     ->> this will use hdfs
> file system.
>
> it uses local file system files and writing to local file system when I
> run in pseudo distributed mode. Since it is single node there is no problem
> of non local data.
> What happens in a fully distributed mode. Will the files be copied to
> other machines or will it throw errors? will the files be replicated and
> will they be partitioned for running MapReduce if i use Localfile system?
>
> Can someone please explain.
>
> Regards
> Sundeep
>
>
>
>
>

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Yes. It&#39;s possible to use your local file system instead of HDFS. As yo=
u said, doesn&#39;t really matter when you are running a pseudo-distributed=
 cluster. This is generally fine if your dataset is fairly small. The place=
 where HDFS access really shines is if your file is huge, generally several=
 TB or PB. That is when individual mappers can access different partitioned=
 data on different nodes improving performance.<div>

<br></div><div>In a fully distributed mode, your data gets partitioned and =
gets stored on several different nodes on HDFS.</div><div>But when you use =
local data, the data is not replication or partitioned, it&#39;s just like =
accessing a single file.<br>

<br><div class=3D"gmail_quote">On Sat, Jan 26, 2013 at 9:49 AM, Sundeep Kam=
bhampati <span dir=3D"ltr">&lt;<a href=3D"mailto:kambhamp@cse.ohio-state.ed=
u" target=3D"_blank">kambhamp@cse.ohio-state.edu</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">Hi Users,<br>
I am kind of new to MapReduce programming I am trying to understand the int=
egration between MapReduce and HDFS.<br>
I could understand MapReduce can use HDFS for data access. But is possible =
not to use HDFS at all and run MapReduce programs?<br>
HDFS does file replication and partitioning. But if I use the following com=
mand to run the Example MaxTemperature<br>
<br>
=A0bin/hadoop jar /usr/local/hadoop/maxtemp.jar MaxTemperature file:///usr/=
local/ncdcinput/<u></u>sample.txt file:///usr/local/out4<br>
<br>
instead of<br>
<br>
=A0bin/hadoop jar /usr/local/hadoop/maxtemp.jar MaxTemperature usr/local/nc=
dcinput/sample.txt usr/local/out4 =A0 =A0 -&gt;&gt; this will use hdfs file=
 system.<br>
<br>
it uses local file system files and writing to local file system when I run=
 in pseudo distributed mode. Since it is single node there is no problem of=
 non local data.<br>
What happens in a fully distributed mode. Will the files be copied to other=
 machines or will it throw errors? will the files be replicated and will th=
ey be partitioned for running MapReduce if i use Localfile system?<br>


<br>
Can someone please explain.<br>
<br>
Regards<span><font color=3D"#888888"><br>
Sundeep<br>
<br>
<br>
<br>
<br>
</font></span></blockquote></div><br>
</div>

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