I'm using backup and recovery 10.1 free. I have created a backup image of my c drive. I now want to create a differential backup. The image is 178gb, on a 250gb drive. If I understand correctly, a differential backup should add in size only what has been created since the last backup, e.g a few mb or very few gb in my case. However, the wizard informs me that the archive will be 178gb in size, and I don't have enough disk space to continue. Why doesn't it tell me that I do have enough space, as the incremental amount to be added is less than 250gb-178gb?