Before attaching, mounting, upgrading ( all the same thing ) a SharePoint content DB from SharePoint 2013 to SharePoint 2016 you MUST test the DB Upgradeblocking errors,
In order to test the content DB run the following PowerShell :
get-spcontentdatabase Test-SPContentDatabase -name WSS_Content_RecallsTest2
The upgradeblocking error like the one below needs to be resolved prior to mounting the DB
Category : LegacySiteDetected Error : True UpgradeBlocking : True Message : 1 site(s) using SharePoint 2010 experience. Remedy : Please upgrade sites using SharePoint 2010 experience in database WSS_Content_RecallsTest2 to SharePoint 2013 experience before proceeding.
When looking into the number of site collections within the content DB I found out that one of the sites is using an older template per the above error:
clear get-spsite -ContentDatabase WSS_Content_RecallsTest http://stage-YourSiteDomain.com/recallsTest 15 http://stage-YourSiteDomain.com/sites/prodsup... 14
the options are :
- Split the content DB
- upgrade the /sites/prodesup… site
- remove the /sites/prodesup… site collection
Upgrade the site :
on SharePoint site collection admin select Site Collection Upgrade.
after upgrading you can run the power shell again to check if all site collection within the content DB are in the same level:
clear get-spsite -ContentDatabase WSS_Content_RecallsTest http://stage-YourSiteDomain.com/recallsTest 15 http://stage-YourSiteDomain.com/sites/prodsup... 15 <---- changed