Hi,

I was confused by the configuration and file system in hadoop. when we create a
FileSystem object and read/write something through it, are we writing to or
reading from HDFS? Could it be local file system? If yes, what determines which
file system it is? Configuration object we used to create the FileSystem object?
When I write mapreduce program which "extends Configured implements Tool", I can
get the right configuration by calling getConf() and use the FileSystem object
to communicate with HDFS. What if I want to read/write HDFS in a separate
Utility class? Where does the configuration come from?

Thanks.

 
-Gang

On May 10, 2011, at 9:57 AM, Gang Luo wrote:
> I was confused by the configuration and file system in hadoop. when we create a
> FileSystem object and read/write something through it, are we writing to or
> reading from HDFS?

Typically, yes.

> Could it be local file system?

Yes.
> If yes, what determines which
> file system it is? Configuration object we used to create the FileSystem object?

Yes.

> When I write mapreduce program which "extends Configured implements Tool", I can
> get the right configuration by calling getConf() and use the FileSystem object
> to communicate with HDFS. What if I want to read/write HDFS in a separate
> Utility class? Where does the configuration come from?

You need to supply it.

Hadoop newbie here,
I have a few of the same questions that Gang has.  I have the single
node configuration installed but every time I restart my computer I
loose my name node because it's location is defaulted to /tmp.  I'm
using 0.21.0.  Is there a write up some where that shows what config
files to change so that the it's not using temp?
Thanks!
JC