Xen virtualization with Novell SUSE Linux Enterprise Server 10 on HP ProLiant servers
Xen is an open-sourced project to provide a server environment to host virtual machines. The hypervisor or virtual machine monitor (VMM) is the software layer that is initially loaded to provide the virtual machine (VM) server functionality. The VMM runs between the server hardware and Linux operating system and is loaded first at boot. Once the VMM has loaded, the Xen VM Server is loaded to create and control the other VMs and communicate with the server hardware. This Xen VM Server is referred to as Dom0 or domain0 and runs in privileged mode. A VM, also referred to as a guest domain (DomU), is an isolated environment running an operating system and applications. This guest domain runs unprivileged. A guest domain may or may not know it is running in a VM, depending on whether it is a para-virtualized or fully-virtualized VM.
A para-virtualized VM means that the VMM has APIs (application program interfaces) to assist in accessing the hardware, and the guest operating system has been modified to know it is running in a VM. The VMM emulates the underlying hardware by presenting virtual devices to the guest operating system. A fully-virtualized VM requires no modifications to the guest operating system, but the VMM must trap and emulate all privileged instructions. For fully-virtualized VMs the physical server must have processors that support Virtualization Technology (VT). HP has VT enabled hardware utilizing both Intel® and AMD™ processors. Fully-virtualized VMs perform slower than para-virtualized VMs.
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