Backup can be made with...
\Apps\7-ZipPortable\App\7-Zip\7z -y %passwordcmd% -w%temp% -x!\Backup\ -x!\Transfer\ -ms=off -r u "%subdest%\%prefix%ref.7z" -u- -up0q0r2x2z1w2!"%subdest%\%prefix%refnew.7z" -up0q3r2x2z0w2!"%subdest%\%prefix%new.7z" "%subsource%"
...where "%prefix%refnew.7z" contains current full backup version of the archive, and
where "%prefix%new.7z" contains the changes of the archive since last backup.
The problem is that "%prefix%refnew.7z" becomes very large and is updated for each backup performed. This takes a lot of time.
Wouldn't it be great to have an option just to store the directory structure, i.e. exclude the file data?
(action 4 and 5 are new)
0 Ignore file (don't create item in new archive for this file)
1 Copy file (copy from old archive to new)
2 Compress (compress file from disk to new archive)
3 Create Anti-item (item that will delete file or directory during extracting). This feature is supported only in 7z format.
4. copy file header from the old archive to new one (exclude file data).
5. store the new file header from disk into the archive (exclude file data).