Adding a Virtual Disk to a Virtual Machine

To add a virtual disk:

Select File > Open and open the virtual machine configuration file (.cfg) you want to modify.
Select Settings > Configuration Editor from the console.
Click the + sign next to IDE Drives or SCSI Devices.
Select the specific device node from the corresponding list (under IDE Drives or SCSI Devices) for where you want to create the virtual disk.
Select Virtual Disk from the Device Type field.
Select a mode for the virtual disk from the Mode field. >> More information on disk modes
In the Name field, enter a path to the location where you want to store information about this virtual disk. Be sure to select a location on your host hard drive.
If you are connecting to a virtual machine on a Linux host and you want to disable write caching, select the Disable write caching option.
In the Capacity (MB) field, enter a maximum size for the disk file.
Click Install.