In the world of Xen paravirtualization, the hypervisor exists in several different forms. A few Xen platforms come with Linux distributions while others don't. Some Xen hypervisors even disguise themselves as different technologies (Microsoft Hyper-V, I'm looking at you.)
Then there is Citrix's Xen offering, XenServer. This article will explain how to install Citrix XenServer and then begin using Citrix's management console, XenCenter.
Choosing a Citrix Xen platform
Citrix offers four different versions of XenServer. The free version is called XenServer Express and can be downloaded from the Citrix website. XenServer Express is an excellent choice for those interested in testing Citrix's basic virtualization offering. You can install XenServer Express on a single server, but you can only manage that one server with it. However, you can install as many virtual machines as the hardware of your server can support. Features such as high availability and live migration are not present in this version for the simple reason that such features require at least two Xen servers.
The most important difference between XenServer Express and the Standard version, the next version above Express, is that the Standard version supports more than one server. In turn, this allows you to manage several physical servers from a single interface.
The next level above the Standard version, Enterprise, allows the user to utilize the live migration feature in order to ease management of virtual machines. Apart from live migration,Enterprise makes it possible manage not just individual servers, but complete resource pools. In addition, XenServer Enterprise can also define quality of service policies, thus ensuring that some virtual machines are allowed more resources than others.
If you are looking for the highest level of data center scalability though, you need XenServer Platinum Edition. This version includes everything necessary to build a virtualized infrastructure with hundreds of virtual servers in a data center. It also has the highest level of support that Citrix offers.
Starting with XenServer Express
Before installing XenServer, make sure that you have the right hardware in place. For most current enterprise servers there should be no problem implementing the software. But if you pull an old server out of the closet to attempt a XenServer installation, the result may be disappointing. The minimal requirements are as follows:
- 1 64 bit 1.5GHz CPU for support of Windows virtual machines with Intel VT or AMT VT (the virtualization support) on the CPU. If your CPU has this feature, don't forget to switch it on in your server BIOS.
- A minimum of 1GB of RAM
- A hard drive with at least 16GB of disk space. Using a dedicated hard disk is highly recommended.
- 100Mbit network card. To use advanced features such as live migration, you need gigabit.
Apart from the requirements for the Xen Server host, you will also need a PC to install the XenCenter management tool. The PC in question has to be a Windows PC, as Windows 2000 or later is required. The other hardware requirements are not very complex. XenCenter will basically run on any Windows PC that has 512 MB of RAM.
If you really want to test the capabilities of XenServer, you'll need a storage area network (SAN). To utilize features such as live migration and work with shared resources pools, and SAN is essential. You don't even need an expensive one either. An alternative would be to build a software SAN solution based on iSCSI and an network file system (NFS) shared directory.
Installing XenServer host
XenServer's need for a dedicated host means that a dual boot is impossible. Therefore the entire server must be dedicated to the XenServer operating system.An example would be Red Hat Linux. There are several different ways to install a XenServer host. For instance, you could use a PXE boot. But for our example, we'll cover a more traditional method and perform a cd-rom based installation.
- Start your server and put the CD-ROM in your optical drive. Make sure the server boots from the CD-ROM.
- Select the keyboard your server is using.
- Choose the install option or upgrade XenServer host. You can also use the installation CD for a physical-to-virtual (P2V) conversion. Next, select OK to indicate that you want to install XenServer on your server. Then accept the licence agreement.
- If the CPU in your server does not offer support for virtualization, you will recieve a warning indicating that you will not be able to install Windows virtual machines (VMs). If you get this message and your CPU actually supports virtualization, make sure to switch it on in your server's BIOS. Otherwise if you want to install Windows VMs, look for another server to use.You may end up being forced to accept the fact that you will only be able to use Linux virtual machines.
- The installer now gives an overview of all available hard disks. To start with, select the hard disk on which you want to install the host operating system (OS). It's a good idea to select the first disk from the list and then press enter to continue.
- After you have indicated which hard drive to install the host OS on, you must tell the installer where to create a reserved storage area for the virtual machine disk files. By default, XenServer will create a storage repository for this purpose. If you wish to perform an easy installation, just put all of the available disk space in this storage repository.
- Indicate from which medium you want to install, as you could have started the installation by PXE-boot as well. Select local media, then OK to continue.
- Now the installation program asks if you also want to install the Linux pack from the second CD-ROM. If you ever plan on doing something with Linux, it's a good idea to install the Linux CD now.
- The installer now asks if you want to verify the installation media. Unless you really don't trust the installation media that you're using, skip this step and press enter.
- Your XenServer will have an administrator who has the name root. You now have to enter the password for this user twice. Remember it well, because you will need it later to connect to your XenServer from the XenCenter management application.
- Next, select the country settings for your server. You need to indicate how you want to use time. There are two options: use the network time protocol (NTP) or enter the time manually. If there is any way of connecting to the NTP hierarchy, select 'Using NTP'. If your server is isolated and there are no ways of connecting to other servers, select 'Manual Time Entry'.
- After selecting the NTP option, specify which NTP server you want to use. If you don't have a local NTP server on your network, pool.ntp.org is a good choice.
- Now indicate which IP address your server has to use. By default, the server will query a dynamic host configuration protocol (DHCP) server for an IP address. This is not a good idea for your XenServer host. After all, you don't want the IP address to suddenly change do you? So select the 'Static' configuration option and next enter IP address, subnetmask and gateway.
- Choose a name for your server as well as the IP address of the domain name server (DNS) you want to use. Select the 'Install XenServer' option to start the installation. This will take a couple of minutes to complete.
- After installing the software from the first installation disk, the installer asks for the Linux support disk. Put it in the optical drive of your server and press enter to continue.
- Finally, once the software has been installed reboot your server. When it is up again, you can connect to it from the XenCenter management console.
Put the installation CD in the optical drive of your server (or download the installation file), double click on the installation file and complete the wizard. When finished, the installer puts an icon on the desktop of your computer which allows you to start XenCenter, as seen in Figure 1.
Figure 1: Use XenCenter to manage your XenServer host.
Now click the Add Your XenServer icon. This opens an authentication window where you have to enter hostname, username and the password of this user. The username will always be the root and the password is the password that you have granted this user during the installation.
Your XenServer host is now up and running. Time to start creating virtual machines, which we will cover in the second part of this series.
About the author: Sander van Vugt is an author and independent technical trainer, specializing in Linux since 1994. van Vugt is also a technical consultant for high availability (HA) clustering and performance optimization, as well as an expert on SUSE Linux Enterprise Desktop 10 (SLED 10) administration.