We are planning to go for a soft launch using a sub domain as well as keeping the old version of the site on the actual domain. We will redirect 1 in 10 users to the new version of the site located at the sub domain in order to pick up any technical or user experience problems. We will then stop using the subdomain and the DNS server will point to the actual domain once the soft launch is over.
We will have some pages with same content on both the actual and the sub domain but since we make use of the sub domain the URLs are going to be different.
I was wondering what sort of an impact that may have on our SEO results and what would be the best approach or advice to minimise the negative impacts of this situation if there are any.