I have a 300gb external drive used to backup my main computer. I use Acronis True Image to make an image weekly, overwriting the existing image each time. I also have a variety of other backup data on there. The Image is about 85gb, and the additional data is another 70gb or so. However my 300 gb drive reports only 40 gb free. My 300gb gross volume nets 279gb usable space, subtracting the 155gb of actual data (85+70) says I should have 124gb available. The fact that 124-40=84 leads me to believe that the image is using (or at least holding) 170gb of space for its 85 gb backup. Disk cleanup shows no files in the recycle bin. Why is that 85gb not being freed up when the image file is overwritten?