Validate the My Site Host and individual My Sites are on a dedicated Web application and separate URL domain.
How to resolve ??
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Cause: The My Site host and individual My Sites are deployed in the same Web application as the root site collection. If the User Profile Service was configured by using the Farm Configuration Wizard, this is how My Sites are set up.
how to resolve the SharePoint Health Analyzer rule "Validate the My Site Host and individual My Sites are on a dedicated Web application and separate URL domain."
Fix: Set up a dedicated Web application, We recommend that you have a separate, dedicated Web application to host the My Site host and individual My Sites. Unless you are using Host-Named Site Collection deployment.
here is step by step instruction to setup MySite... http://myspexp.com/2010/06/14/setting-up-mysite-as-a-different-application-2/