Okay, I think that Windows automatically handles this, but I could be wrong. Regardless, you can, in general, increase RAID systems' sizes by adding new disks (I sure that there are implementations that don't allow that, but I doubt they're common). However, increasing the size of the (pseudo-)physical disk won't automatically increase the size of the filesystem on it. That is, most filesystems create a static amount of storage when they're initially created, based on how much physical space they have available. When you increase the amount of physical space, the filesystem is not necessarily going to know to increase it's size, as well. But, then again, Windows might automatically detect that and Do The Right Thing^TM. Most OSes won't (for good reason).