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• Operating systems not optimized for the virtual machine environment are often
called shrink-wrapped, out-of-the-box, unmodified, or fully-virtualized guest.
23.4 Virtual Machine Modes
The VM Server hosts virtual machines running operating systems in one of two modes:
fully virtual or paravirtual.
• Fully virtual: Complete emulation of all hardware devices. Although it requires
special computer hardware, most operating systems can run in fully virtual mode
because the VMM emulates all computer devices to fool the operating system into
thinking it has exclusive access to an entire computer. This complete emulation of
computer hardware demands more CPU resources from the VM Server. As a result,
an operating system running in full virtualization mode runs slower.
• Paravirtual: Selective emulation of hardware devices. An operating system that is
optimized for the VMM is said to be VM-aware and can run in paravirtual mode.
Paravirtual mode does not require complete emulation and therefore requires less
management overhead. For example, VM-aware operating systems do not require
an emulated graphics card, so the VM Server does not need to emulate video data.
As a result, an operating system running in paravirtual mode demands fewer CPU
resources and has better performance. It also requires no special computer hardware.
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.
Virtual Machine Server
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Troubleshooting
