Any manual action requires that all users be logged off of the SQL Server resources.
Local processes that have read-only access to volumes do not prevent removal of a resource from service but may cause a restore to fail when you try to switch back. Examples might be the Performance Monitor, which periodically polls each volume, or any running process which is installed on the shared or replicated volume. You can minimize your potential for this type of restore failure by installing the Microsoft SQL Server on local drives and putting only the database on shared or replicated volumes.
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