Problem after deleting Mirrored Volume

I am facing a problem that when i creat mirrored volume of my system partition on other free space. it is created. But when i break mirror set after that system does not allow me to delete mirrored volume other than the original system volume. it shows a message that system volume can not be deleted. But in my system i have already a system volume. so tell me that how can i delete it. Pls give me help.