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I'm totally new to hadoop and just finished installing which took me 2 days... I'm now trying with the hadoop dfs command, but i just couldn't understand it, although i've been browsing for days, i couldnt find the answer to what i want to know. All the examples shows what the result is supposed to be, without explaining the real structure of it, so i will be happy if someone could assist me in understanding hadoop hdfs. I've created a directory on the HDFS. bin/hadoop fs -mkdir input OK, i shall check on it with the ls command. bin/hadoop fs -ls Found 1 items drwxr-xr-x - hadoop supergroup 0 2012-07-30 11:08 input OK, no problem, everything seems perfect.. BUT where is actually the HDFS data stored? I thought it would store in the my datanode directory (/home/hadoop/datastore), which was defined in core-site.xml under hadoop.tmp.dir, but it is not there.. Then i tried to view through the WEB-UI and i found that "input" was created under "/user/hadoop/" (/user/hadoop/input). My questions are (1) What are the datanode directory (hadoop.tmp.dir) used for, since it doesnt store everything i processed through dfs command? (2) Everything created with dfs command goes to /user/XXX/ , how to change the value of it? (3) I cant see anything when i try to access through normal linux command (ls /user/hadoop). Does /user/hadoop exists logically? I'm sorry if my questions are stupid.. a newbie struggling to understand hadoop better.. Thank you in advance.

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