Xen is a bare-metal or Type 1 hypervisor that will create logical pools of system resources so that many VMs (virtual machines) can share the same physical resources. Xen allows users to run multiple operating systems on host computers to enable virtualization. Xen lets the user share the hardware resources of the same system among multiple operating systems concurrently. Users can run multiple operating systems on the same hardware resources.
XenServer installs directly on bare-metal hardware avoiding the overhead, complexity, and performance bottlenecks of an underlying operating system. XenServer will use the device drivers available from the Linux kernel. So that XenServer can run on a wide variety of storage and hardware devices. However, Citrix recommends that the users use certified device drivers. The XenServer host consists of the following components:
- The Xen Hypervisor: The Xen hypervisor is the basic abstraction layer of the software responsible for low-level tasks such as CPU scheduling and memory isolation for resident virtual machines. The Xen hypervisor abstracts from the hardware for the virtual machines. The hypervisor does not know about networking, video, external storage devices, etc. The Linux Foundation Xen Project community will develop and maintain the Xen hypervisor as free software licensed under the GNU General Public License. XenServer 7.1 uses version 4.7 of the Xen hypervisor.
- The Control Domain: The control domain is also known as dom0 or Domain0. The Control Domain is a privileged and secure Linux virtual machine (based on a CentOS 7.2 distribution) that will run the XenServer management toolstack. Besides providing the management functions, the Control Domain also runs the driver stack that offers user-created VM access to the physical devices.
- The management toolstack: The XenServer management toolstack is also known as xapi