Prevent a folder to be indexed in desktop client with VSF


Does someone know a working solution to prevent a folder (preferable a external datastore) to be synced/indexed by the desktop client?

I would like to offer to users a external storage mapped as folder containing a ton of files (millions) and I am afraid that this slows down the desktop sync (VSF). Also - simply that folder does not need to be accesible on the desktop.

Many thanks