Prepare input data for Hadoop

[Huy Phan]

Hi all,

I have a question about strategy to prepare data for Hadoop to run their 
MapReduce job, we have to (somehow) copy input files from our local 
filesystem to HDFS, how can we make sure that one input file is not 
processed twice in different executions of the same MapReduce job (let's 
say my MapReduce job runs once each 30 mins) ?
I don't want to delete my input files after finishing the MR job because 
I may want to re-use it later.