Question about Ultimate

I want to purchase ultimate and combine my eCommerce sites.

But I want to know how the database works. If I have sites on different servers, will they all be hitting the database on one server? Will that bog down the store on that server?

Or do all the stores need to be on the same server?

As I understand it (used to be but may have been changed) all sites must be on the same server (or cluster). I.e. all database need to be accessible from 'localhost' on the primary site.

As tbirnseth said, the stores must all be on the same server, and technically even on the same plan in most cases. The domains or subdomains of the sub stores are merely redirected back to the main “store” folder via .htaccess files, but keep their own identity through the redirect.

Thanks, guys. Good to know.