Hello, Does it will effect overall speed (particularly Initial loading speed of website) if we run two different domains as Parent Portals. Or is it advisable to run two different independent Portal under two different DNN installation ? Regards Pooja

Running two portals within a single instance of DotNetNuke should not result in performance issues, provided that your server/database can handle the total traffic.

There may be other reasons (you don't want to mix users or data) to separate the portals, but that is a different consideration.