I back up my video projects onto a WD 2TB Green drive and I've got about 250GB free. I forgot how much space is needed to leave empty so the drive doesn't slow down or freeze up. Was it 10% free? I have another project (60GB) to transfer to the Green drive but am not sure if I can get away with putting in on there or if I need to buy another HDD. I did a quick search and read that some folks leave 20% or 50% free, but that was for the startup disk with the OS on it. My drives are strictly for storing video/photo projects after the project is completed. Any input is appreciated.