Regarding Xen as a tool for Openstack deployment ( like VMWare Workstation) :-
Xen is bare metal Hypervisor, so you can create Xen Paravirtual VMs (DomUs) , running Ubuntu 14.04
(or CentOS 7) to host Controller,Network,Compute Openstack nodes.
Domain 0, a modified Linux kernel, is a unique virtual machine running on the Xen
hypervisor that has special rights to access physical I/O resources as well as interact with
the other virtual machines (Domain U: PV and HVM Guests) running on the system. All
Xen virtualization environments require Domain 0 to be running before any other virtual
machines can be started.
Two drivers are included in Domain 0 to support network and local disk requests from
Domain U PV and HVM Guests (see below); the Network Backend Driver and the Block
Backend Driver. The Network Backend Driver communicates directly with the local
networking hardware to process all virtual machines requests coming from the Domain U
guests. The Block Backend Driver communicates with the local storage disk to read and
write data from the drive based upon Domain U requests.
Next
Domain U
DomainU guests have no direct access to physical hardware on the machine as a
Domain0 Guest does and is often referred to as unprivileged. All paravirtualized virtual
machines running on a Xen hypervisor are referred to as
Domain U PV Guests
and are
modified Linux operating systems, Solaris, FreeBSD, and other UNIX operating systems.
All fully virtualized machines running on a Xen hypervisor are referred to as
Domain U
HVM Guests
and run standard Windows or any other unchanged operating system.
The Domain U PV Guest virtual machine is aware that it does not have direct access to
the hardware and recognizes that other virtual machines are running on the same
machine. The Domain U HVM Guest virtual machine is not aware that it is sharing
processing time on the hardware and that other virtual machines are present.
A Domain U PV Guest contains two drivers for network and disk access, PV Network
Driver and PV Block Driver
For further details view http://www-archive.xenproject.org/fil...