Virtualization using XenEnterprise with Dell PowerEdge Servers and ...

1 Introduction
Server Virtualization is fast becoming a fore-front technology in datacenters. Dell
PowerEdge servers and storage coupled with XenEnterprise software from
XenSource provide a compelling solution to realize a scalable and dynamic virtual
datacenter. This paper describes an overview of XenSource’s XenEnterprise virtualization
software and the installation and configuration steps for XenEnterprise on Dell PowerEdge
servers and using Dell OpenManage to manage the XenEnterprise hosts.
2 Virtualization with Xen
2.1 Open Source Xen Hypervisor
With Xen virtualization, a thin software layer known as the Xen hypervisor is inserted
between the server’s hardware and the operating system. This provides an abstraction layer
that allows each physical server to run one or more “virtual machines” or “guests”,
effectively decoupling the operating system and its applications from the underlying
physical server.
Xen enables IT managers to increase utilization of server resources, achieve server
consolidation, scale their test & development environments, and achieve greater business
continuity through dynamic provisioning.
2.2 Paravirtualization vs. Emulation-Translation Virtualization
First generation hypervisors present each virtual machine with an emulated hardware layer
that offers the guest operating system the illusion of a standard server with well-known
hardware devices. When a running guest attempts to control the hardware using privileged
instructions, the hypervisor stops execution and emulates the legacy hardware device,
hiding the real hardware underneath. It then patches the operating system code of the
running guest, in real time, to make its future hardware accesses virtualization safe. Of
course, this complexity impacts performance, much as emulated floating-point computation
did prior to the implementation of hardware floating-point support.
The Xen hypervisor introduced a powerful virtualization architecture called
paravirtualization, pioneered by the XenSource founders. Paravirtualization can deliver
near-native performance to virtual machines while ensuring that physical resources are
fairly shared between them.
In Xen, guests interface with the hypervisor via the hypercall API, rather than through
hardware emulation. This allows the hypervisor and operating system to cooperate to
optimally virtualize the underlying hardware and schedule guest CPU and I/O, resulting in
outstanding performance, security and portability.
Dell Inc. 3 www.dell.com/virtualization