Xen 01 - The basics of XEN virtualisation

category: learnz/xen · date: 2007-12-29 · source: old.linuxor.sk/VIRTUALIZATION/BASIC/bh_xen.txt · theme: github

The Slovak original of this document: Xen 01 - Základy XEN virtualizácie (slovensky).

asciiart

|=----------------------------------=[ XEN ]=------------------------------=|
+---------------------------------------------------------------------------+
|                                                                           |
|                                      XEN                                  |
|                                                                           |
+---------------------------------------------------------------------------+
|=-------------------------------=[ BH 2007 ]=-----------------------------=|

1. Basic terms

asciiart

        Xen is a hypervisor (virtual machine monitor, VMM) for x86-compatible PCs.
        Xen can safely run several virtual machines, each of which can
        run a different OS. All of that on a single physical system with
        performance close to native speed.

        Xen virtualisation - basics
        ---------------------------
        * dom0 : a server with a xen kernel on which the virtual machines run (linux, bsd)
        * domU : a virtual machine, either paravirtualised or hardware-virtualised
        * paravirtualisation : virtualisation in which the guest OS is modified so that it can run as a virtual machine.
        * hardware virtualisation, HVM : lets an unmodified OS, Windows for instance, run. Needs processor support: SVM or VT
        * SVM : Secure Virtual Machines, hardware virtualisation from AMD, known as Pacifica
        * VT : hardware virtualisation from Intel
        * xm : Xen management, the program for managing XEN machines
        * virsh : virtual shell, a frontend for xm for controlling virtual machines (Xen and other virtualisation engines)
        * virt-manager : a GUI giving a view of the virtual machines on one dom0 host

        Xen virtualisation - network
        ----------------------------
        * ethX : a physical interface (in a domU, ethX names the ordinary network interfaces)
        * vethX: a logical interface
        * vifX.X: a virtual interface

2. Limitations

asciiart

        Xen 3 allows only three network interfaces in a domU
        Xen 3.1 supports 8 network interfaces in a domU

        XenEnterprise is built on the 64-bit Xen, which allows up to 128 GB of physical memory.
        XenServer is also built on the 64-bit Xen, which allows up to 128 GB of physical memory.
        XenExpress is also built on the 64-bit Xen, but is limited to 4 GB of physical memory.

        XenEnterprise can use up to 32 physical CPU sockets, each CPU can have 32 cores
        XenServer can use up to 32 physical CPU sockets, each CPU can have 32 cores
        XenExpress can use 2 physical CPU sockets, each CPU can have 8 cores

        XenEnterprise and XenServer allow 50 virtual machines to run on one server at once.
        XenExpress supports running 4 virtual machines at once.

3. Installing dom0 - Debian 4.0

asciiart

        BH_Debian4.0_XEN_dom0.txt

4. Installing domU - Debian 4.0

asciiart

        BH_Debian4.0_XEN_domU.txt

X. Linkz

asciiart

        GUI for XEN
        -----------
        http://www.enomalism.com/

        Automating Xen Virtual Machine Deployment
        -----------------------------------------
        http://howto.krisbuytaert.be/AutomatingVirtualMachineDeployment/

        Networking
        ----------
        http://wiki.xensource.com/xenwiki/XenNetworking
        http://wiki.xensource.com/xenwiki/XenNetworkingExamples

        XEN on DEBIAN dom0
        ------------------
        http://www.howtoforge.com/debian_etch_xen_3.1

        XEN on DEBIAN domU
        ------------------
        http://wiki.xensource.com/xenwiki/DebianDomU

        Debian and XEN
        --------------
        http://wiki.xensource.com/xenwiki/DebianPackageMaintenance

        Tested systems, storage, components and drivers for XEN
        -------------------------------------------------------
        http://hcl.xensource.com/?showall=yes&subtab=systems
        http://hcl.xensource.com/?showall=no&subtab=storage
        http://hcl.xensource.com/?showall=no&subtab=components
        http://hcl.xensource.com/?showall=no&subtab=drivers

        Companies providing virtual machines
        ------------------------------------
        http://www.budgetdedicated.com/
        http://wiki.xensource.com/xenwiki/VirtualPrivateServerProviders

        Other
        -----
        http://wiki.xensource.com/xenwiki/XenFaq
        http://www.linuxjournal.com/article/8909
        http://www.root.cz/clanky/klonovanie-tucniaka-alebo-virtualizacia-v-linuxe-dalsie-projekty/

        Virtual cluster on XEN
        ----------------------
        http://www.clustermonkey.net//content/view/139/33/
        http://www.clustermonkey.net//content/view/139/33/1/1/

        Video - XenEnterprise v4 features
        ---------------------------------
        http://bits.xensource.com/training/400/mini_training/v4_mini_product_training.html

Current practice (checked 2026-10)

noteThe article above is kept as it was written in 2007. This section lists what has changed since and what to do instead today.

xm and xend: the article names xm as the management program. The Python toolstack (xend and xm) was deprecated in Xen 4.3 and removed in Xen 4.5; the tool is now xl, which talks to the hypervisor through libxl and needs no xend daemon. Most xm subcommands have an xl twin with the same name.
virsh and virt-manager: they are described as a frontend for xm. They still exist, but libvirt now drives Xen through libxl, not through xm/xend.
Guest types: the article knows two, paravirtualised (PV) and HVM. There is a third one today, PVH: a PV-style guest without emulated hardware that runs inside the CPU's hardware virtualisation extensions (VT-x or SVM). Use type = "pvh" in the guest config when the guest kernel supports it.
32-bit PV guests: the 32-bit PV guests this series builds are, per the Xen support statement, security supported only when run inside the PV shim. Build new guests 64-bit.
Limitations: the numbers in section 2 describe Xen 3 and the XenSource products of 2007 (XenEnterprise, XenServer, XenExpress). Do not plan with them; the current limits and the support status of each feature are in SUPPORT.md of the Xen release you run.
Debian 4.0: Etch reached end of life on 2010-02-15. Sections 3 and 4 point to the dom0 and domU articles of this series; their "Current practice" sections say how Debian packages Xen today.
Links: the wiki.xensource.com addresses are from the XenSource era. The project documentation is now at wiki.xenproject.org and the man pages at xenbits.xen.org/docs.

Sources: