In Hadoop where does the framework save the output of the Map task in a normal Map-Reduce Application?

Question

I am trying to find out where does the output of a Map task is saved to disk before it can be used by a Reduce task.

Note: - version used is Hadoop 0.20

Answer 1

Task tracker starts a separate JVM process for every Map or Reduce task.

Mapper output (intermediate data) is written to the Local file system (NOT HDFS) of each mapper slave node. Once data transferred to Reducer, We won’t be able to access these temporary files.

If you what to see your Mapper output, I suggest using IdentityReducer?