Parallelize downloads across hostnames?

Question

Google

Tell me how to implement Parallelize downloads across hostnames
Google page speed swears at static resources .. for example, pictures.
I understood from the help that it is required to transfer to another domain.
Well, for example, I will create virtual hosts, specify the folder of the main site

media0.site.ru 
media1.site.ru

document root
/var/www/site.ru
and then the question is, how not to duplicate media0 media1 with the main site later, because the robots will then say 3 takes for me ...