There seems to be a lack of information out there regarding upgrading SharePoint 2010 My Sites to SharePoint 2013.
If you try to do a straight “Mount-SPContentDatabase” to a new web application. This will work partially, as you will be able to get to your “My Site”, however, when trying to go into “Site Settings” or “Site Permissions”, you will get a “404 – File Not Found” for a lot of the back-end system files.
The best way I have found is to set up the My Site Host first in SharePoint 2013, and then run a Mount-SPContentDatabase on your old SharePoint 2010 My Sites database.
1. Backup your WSS_Content_UserSites
2. Restore it to your SharePoint 2013 SQL as a new database
3. In Central Admin, go to “Application Management”, “Manage Web Applications”, choose “New”
4. Once the site is created, choose to “Create a new site collection”, and select the “Enterprise” tab, and “My Site Host” as the type.
5. Once the My Site Host is created, you can attach your 2010 My Sites database:
Mount-SPContentDatabase -Name WSS_Content_UserSites -WebApplication https://mysites.contoso.com
6. Finally, go into your User Profile Service (Application Management -> Manage Service Applications -> User Profile Service). Click on “Setup My Sites”
7. Enter your My Site Host in the area provided, and don’t forget to add the appropriate groups to “Read Permission Level”