A spanned volume is used to combine unallocated space from different physical disks. Unallocated space on up to 32 physical disks can be combined to create a single spanned volume. The amount of space used on each disk can be different, and data is written to each volume in sequence, starting with the first volume. When space on the first volume fills, space on the next volume is used, and so on. You can extend spanned volumes to unallocated space as necessary to provide additional storage capacity. Like Simple Volumes, Spanned volumes also provide no fault tolerance. If one of the disks of which the spanned volume consists fails, the entire volume fails and data must be recovered from backup.
Because of how data is written to spanned volumes, they offer poor performance and no fault tolerance. You cannot extend or span the system volume. Nor will Windows allow you to install the operating system on a spanned volume.