Hello @Anonymous , Thanks for reaching out and sorry for delayed response.
Deploying Azure AD Connect against an existing ADSync database is only supported with full SQL. It is not supported with SQL Express LocalDB. If you have an existing ADSync database in LocalDB that you wish to use, you must first backup the ADSync database (LocalDB) and restore it to full SQL. After which, you can deploy Azure AD Connect against the restored database using this method.
The version of the Azure AD Connect used for installation must satisfy the following criteria:
- 1.1.613.0 or above, AND
- Same or higher than the version of the Azure AD Connect last used with the ADSync database. If the Azure AD Connect version used for installation is higher than the version last used with the ADSync database, then a full sync may be required. Full sync is required if there are schema or sync rule changes between the two versions.
Refer this article to know all supported scenarios and prerequisites for Install Azure AD Connect using an existing ADSync database.
But, if you still have access to your Azure AD connect environment then you could use this alternative approach which help you to Import and export Azure AD Connect configuration settings and then install Azure AD connect on new server to have identical configuration.
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