Attached disk does not appear in FreeNas UI disks section, but after create a volume it does, why?

When I attach a disk to my FreeNAS it does not appear in the user interface under the disks section when I click "View Disks".

However, if I attempt to add a volume then I can select the disk in the volume manager and create a volume. Then after the volume has been created I can see the attached disk.

Is this how it is supposed to behave or is it a bug? Regardless, why does the disk appear in the volume manager but not in the disks section?

I followed the source code of FreeNas and found in notifier.py it does disks = self.sysctl('kern.disks').split() which is equivalent to sysctl kern.disks Linux command. It does this to find the attached disks as per the volume manager.

For the disks view, I have not yet investigated.