I'm currently learning Qt and have decided to write a little application to backup important documents each month to DVD. My current design makes use of the 7zip library along with cdrtools (mkisofs and cdrecord) to compress the directories into a spanning zip archive comprising of zip files each the size of a DVD and then use mkisofs to create a disk image.
The problem with this design is that it will require a lot of free disk space (the compressed size of all your important documents and at least 1 DVD image). If the bulk of the files are already highly compressed such as JPEGs it looks as though the user will only be able to use up half their hardisk space before running out of room for the backup utility to do its job.
However, I want to be able to span the files over multiple disks because if the user has very large files such as videos they wont utilise the full DVD capacity or it might not fit on at all - e.g. the user has a 10 GB file to backup.
Does anyone have any suggestions for how I can create a set of DVD images which utilise the disks' full capacities without requiring an infeasible amount of temporary hardisk space?