Clicking the SmartMove tab brings up the SmartMove window.

Check Enable SmartMove to enable the SmartMove setting to help reduce the resynchronization time for mirror operations and subdisk moves. SmartMove reduces the resynchronization time by using the NTFS or ReFS file system metadata to resynchronize only those regions that the NTFS or ReFS file systems use. When SmartMove is not enabled, SFW resynchronizes all regions.