I have a multi site network wordpress blog. There are the following sites
domain.com
domain.com/blog2
domain.com/blog3
When I upload files for domain.com they will be in domain.com/media. That is how I want it. But when I upload files for blog2 (or blog3) they will be in domain.com/blog2/files/ (or domain.com/blog3/files/). I can change the file folder for every site in site settings (admin - settings - miscellaneous). I also was able to set not to use the upload date and everything, but regardless what I do, the files will be in /blog2/files (I entered an other folder: /media).
How can I archive that all files will be stored in domain.com/media and all sites are able to choose the files from there?
Just tell Wordpress to store the medias files in an absolute folder.
Go to Settings > Medias > Uploading Files and paste the full absolute path corresponding to domain.com/media (where it says "Default is wp-content/uploads")
It can be something like /var/www/domain.com/media e.g, it really depends on your hosting. Obviously it should be readable/writable as well.
Hope this helps !