A customer ask us to reduce data base size, but all projects are still active.
Someone have an idea to achieve this?
may be dropped old version from DB (remove data from blob column)
move project to archive.
Create new Project and create baseLine with last version for all elements
If all the projects are still active, then no, I don't believe there is anything you can do as it stands.
As suggested, you need to migrate current development effort to new projects and then you will be able to archive the old ones using the supplied archiving tool, which will delete the blob data from the database.