"fdisk -l" is the command to check current disks .
To add a Disk , Right Click on the server >> click on Settings/Edit settings as below .
Then it will prompt to below screen , Then select Hard Disk and click on Add as shown below .
Click on Next as shown below
Specify the Size as you needed . In below example I have mentioned 1Gb and then click on Next.
Then click finish as show Below .
Then once you scan the Disks you can see the new disk from the OS.
Syntax :- echo “- - -“> /sys/class/scsi_host/host?/scan
Below you can see new Disk was discovered after scan the hosts .