I am migrating from SP2010 to SP2013 farm. In the old farm web applications are using Window Classic mode. I was told to follow the procedure here (http://technet.microsoft.com/en-us/library/gg251985(v=office.15).aspx). Hence I followed the section "Convert SharePoint 2010 Products classic-mode web applications to SharePoint 2013 claims-based web applications"
My first question is, why I need to perform conversion steps? I am not feeling comfortable because my users can login to new farm without perform above steps.
In order to follow best practice, I followed and when I run
Convert-SPWebApplication –Identity yourWebAppUrl –To Claims -RetainPermissions
It returnes warning:
WARNING: The conversion of web application and most of the users to Claims mode is completed. However, one or more users could not be converted to Claims mode. Refer to the ULS logs for the details. For the troubleshooting tips refer to the http://go.microsoft.com/fwlink/?LinkID=236943 article.
It even not giving me the correlection number so I am unable to track what went wrong. However I can login to the site with several users (I have hundred users and unable to check 1 by 1)
My second question is, do I need to worry about the warning?