compressing hard will decrease system performance,, compressing an compressed data will affect more performance..
try this if you wish to use
apart from these there's an software called KGB Archiver(it take long time to compress & decompress it again http://kgbarchiver.net/
my personal suggestion it 10 gb hard it not enough for current situations.. a small stamp sized flash drive for 64 & 128 gb are in market..
hdd upto 2 Tb are available..
if money is you prob try to get used hdd from ebay or other wesite