Is there an additional overhead when storing data in HDFS?

[WangRamon]

Hi All I'm wondering if there is an additional overhead when storing some data 
into HDFS? For example, I have a 2GB file, the replicate factor of HDSF is 2, 
when the file is uploaded to HDFS, should HDFS use 4GB to store it or more then 
4GB to store it? If it takes more than 4GB space, why? ThanksRamon