|How much space do I need when saving an image ?|
|This really depends. It depends on the data on a partition, and the compression algorithm you choose.|
Normally if you choose to use gzip, and the partition is an OS (GNU/Linux, MS Windows) partition, the space required is about 1/3.
E.g. For 45 GB data used on a 100 GB harddrive, you will need about 15 GB space to save the image.