On the wizard page (by default), only the disk you are most likely to use is shown. In the list below, all the disks that ...

On the wizard page (by default), only the disk you are most likely to use is shown. 
In the list below, all the disks that are attached to this server are shown, both internal and external disks. The list excludes critical disks that contain system files, and cluster shared volume disks.

Select the check box for a disk to make it appear in the list of available disks in the wizard page.