Incremental and Differential Images
Starting from version 4.0 there are 3 types of image which you must select when creating a new backup – full, incremental and differential.
Full backup includes all data and similar to previous images (but image file format has been changed). Incremental and differential are based on the previous image and include only data changed since the last backup.
Such previous image is called a base image and can be a full backup or another incremental image. If for particular block there's no difference between current state and base image, data is not written into the current image but a reference to a base image is placed instead. Differential image differs from incremental in the matter of allowing only a full backup to be a base image.
The base image and all subsequent incremental images have the same partitions backed up. The create wizard dialog for incremental image shows the partitions selected for information purposes only; it does not allow to change the selection. If it appears that partition included into base image is no longer available or reformatted, the warning must be shown and the image creation seized.
Password if any is shared between all images and cannot be changed in incremental image. All other options like compression, file splitting, and description are individual for every image.
Normally incremental images are named by the date/time of creation and located in the folder below the full backup, so the file structure will be as follows:
<Images location>\<Full backup> <Images location>\<Full backup>\<Incremental 1> <Images location>\<Full backup>\<Incremental 2>
When you select any image as a base for incremental image, the application scans the parent folder and sibling folders (if it is not a full backup) or children folders (for full backup selected).
All found images are enumerated and shown as a list from which user can select a required base image. If more than one image with the same sequence exists, it will be ignored. For example, the full backup has sequence #0, the first incremental image will have sequence #1. If another incremental image is created based on #0, it will become #1 again, so one of them will be ignored during the enumeration.
When an incremental image is selected for restoring, all sequence images starting from full backup and including the selected image must be presented in the folders as described above.
Backward image compatibility is supported but forward is not. All new images created will have new image format.