Combine the space of 2 drives for space check


I have an application that uses 2 drives to write data as a combined volume. For Example, drive Y and Z are the combined storage for the images. If y fills up, it will keep on writing to Z and will later, as the files age, it will clean up both drives. If both drives fill up it will clean up both drives. So I have the potential of 0 space on one drive and plenty on the other so it will not stop writing to the combined drives. Can I have a drive_check alert on the combined space of 2 drives so I am not getting alerts when only one is full? We are running on windows 2008 and 2012.