23.5. Virtual Machine Server

The virtual machine monitor (VMM) runs between the server hardware and the SUSE Linux operating system kernel. When the computer boots, the VMM loads first and then starts the VM Server in privileged mode, which means that the VM Server has ability to create and control virtual machines and has direct access to the computer hardware. The VM Server is configured with native device drivers that match the actual devices in the computer. For example, if the computer has a physcial e1000 network card, the VM Server is configured to load and run the SUSE Linux device driver for the e1000.

Figure 23.1. Virtual Machine Server and Device Drivers

Virtual Machine Server and Device Drivers

Virtual machines are defined and stored on the VM Server. The definitions (called VM definitions) are stored in a configuration file located at /etc/xen/vm/vm_name. The configuration file defines the virtual resources, such as CPU, memory, network card, and block devices, the operating system sees when it is installed and booted on the virtual machine.

Figure 23.2. Virtual Machine Definitions and Virtual Machine Monitor

Virtual Machine Definitions and Virtual Machine Monitor

In both full virtualization and paravirtual modes, a VM’s operating system uses device drivers to interact with the VMM. In full virtualization mode, the operating system uses its native OS device drivers for a standard set of emulated devices, such as an AMD PCNet or NE2000 network card, an IDE disk drive, and a VGA graphics card. In paravirtual mode, the VM-aware operating systems include special device drivers (called Xen drivers) to communicate through the VMM and VM Server to the physical devices in the computer.

Figure 23.3. VM Device Drivers

VM Device Drivers

If, for example, a VM’s operating system running in full-virtualization mode needs to save a file on its virtual 20-GB disk drive, the operating system passes its request through the device driver to the VMM. The VMM understands which portion of the 500-GB physical disk the VM has access to and passes instructions to the VM Server. The VM Server accesses the disk drive and writes the file to the pre-defined location on the 500-GB disk.

Depending on your computing needs and available computer resources, any number of VMs can be created and can simultaneously run on the VM Server. The operating system of each VM interacts independently with the VMM and VM Server platform to consume virtual or emulated CPU, memory, block device, and network resources.

Figure 23.4. VM Server and Virtual Machines

VM Server and Virtual Machines

VMs can be viewed and managed from the VM Server desktop.

Figure 23.5. VM Server Desktop and Three Virtual Machines

VM Server Desktop and Three Virtual Machines