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

In the wizard page by default, only the most likely to use disk is shown. In the list below, all the disks that are attached to this server are shown. The list includes both internal as well as external disks (if any) and it excludes critical disks containing system files.  Select the check box for a disk to make it appear in the list of available disks in the wizard page.