You might be wondering how to Migrate AAD Connect Database to New SQL Database, you might have searched Documentation from Microsoft but found none. I guess its not supported and what you need to do is install a new instance and run it in Staging Mode, I had tried this and it works really well but if this option is not good for you for some reasons then here is a non-supported guide on how to Migrate your AAD Connect Database to New SQL Database in few easy steps.
Stop and Disable “Microsoft Azure AD Sync” or AD Sync Service.
Open your Services.msc, locate Microsoft Azure AD Sync, right click on it then stop the service.
Migrate your old ADSync Database to new SQL server
First Back Up your database, then restore it on a new SQL Server Instance. Check the Collation, Service Account Name and Permissions, it should all be the same.
Export your Registry Settings
You can skip this if you trust me 🙂
This is just a fail safe mechanism if things go wrong.
There are two configurations items to backup:
Update Registry with new SQL Server Details.
Update ADSync Parameters Section, Server and SQL Instance if you use one otherwise leave it blank
Update MSOLCoExistence Section, Server and SQL Instance if you use one otherwise leave it blank
Enable and Start “Microsoft Azure AD Sync” or AD Sync Service.
Check Event Viewer for Logs
If you get Sync Errors like this, you might need a restart like what happened to me
After restart it when everything is set up correctly logs should show Finished