XenServer 5: First Impressions

Putting XenServer 5 through its paces; getting hands-on with Citrix's latest virtualization solution.

Can 99% of the world’s cloud vendors be wrong? Is XenServer and its hypervisor technology the right answer for you and your virtual infrastructure? I’m taking XenServer 5 for a test drive to view it from a new user’s perspective and to answer these questions. This test drive begins with ISO image and software downloads from the Citrix website, proceeds through installation and update and ends with working with virtual machines (VMs). My purpose is to give you an overview of XenServer’s features and possibilities for your own trek into the world of virtualization.

The test hardware for this article is an AMD 64×2 4800+ with 3GB RAM and internal IDE and SATA hard drives.

Download and Installation

XenServer 5 is easy to find on the Citrix homepage — follow the link to the download area. At a minimum, you’ll need the XenServer 5 ISO, XenCenter 5, and the license to update your system from the Express Edition to the Enterprise Edition. Optionally, you might want the 250MB Linux Guest Support ISO file. This ISO image contains Linux VM templates and other useful tools for Linux VMs.

Save the license file (XenServer-free-license.xslic) from the download area onto your XenCenter Windows computer. This license enables you to use XenServer Enterprise Edition until April 23, 2009. The unlimited license key update will be available on March 25, 2009.

Once you download the 300MB XenServer ISO image and burn it to a CD-R, installation takes 15 to 20 minutes including the reboot and login to the XenServer Console (Shown in Figure 1). If you downloaded and burned the Linux Guest Support ISO image to a CD-R, the installer process prompts you for it.

Figure 1: XenServer Console Configuration
Figure 1: XenServer Console Configuration

Local and Remote Consoles

XenCenter allows the most flexibility and feature rich experience for managing your virtual infrastructure. There are, however, two other consoles available to you; local and remote. The local console is available on the hypervisor computer itself. Enabling the remote shell service (SSH) provides you with shell (command line) access to the XenServer system and a duplicate of the Xen Console. To use the remote console, SSH to the XenServer computer, login and issue the xconsole command to invoke the console.

Using either the remote or local XenServer Console, you have limited functionality — in other words, you can’t fully manage a Xen hypervisor with one of these consoles but they provide important information about your system. For example, you enable SSH access via the consoles but you can’t create virtual machines with them. You have to use Xen Center for complete management capabilities and options. See Figure 2 for a look at XenCenter 5.

Figure 2: XenServer GUI
Figure 2: XenServer GUI

XenServer 5 Features

  • Bare-metal Hypervisor
  • 8 Maximum Virtual CPUs
  • Windows and Linux VMs
  • Unlimited VMs
  • Unlimited Memory
  • P2V & V2V Conversion
  • Centralized Management
  • Live Motion
  • VM Template Library
  • Centralized Configuration Management
  • Patch Management
  • Intelligent Maintenance Mode
  • Intelligent VM Placement
  • Fine-grained CPU Resource Controls
  • Hot Swappable Disks and NICs

Virtual Machine Management

There are three ways to create VMs in XenCenter 5: Template, Import and ISO Image. The template method is by far the most efficient in terms of speed and configuration consistency. Anyone managing a Xen environment should implement operating system templates for all new VMs. When creating a template, remember to give the template image a generic hostname and a dynamic IP address to remove the possibility of duplicating one or the other on your network.

Creating a template from a “gold” or master image is an irreversible process so if you realize later that you’ve made a mistake in your master image, you’ll have to create a VM from the template, uninstall the template, fix the problem in the image and convert it once again to a template.


Managing updates is awkward at best. To install updates, you have to download them onto your XenCenter (Windows) system then apply them using XenCenter under Tools->Updates Manager. Update configuration and management should be handled via a yum-style repository in an automated fashion. Another alternative is to configure update management similar to Windows updates with multiple possibilities such as download only, download and install and notify only.

Creating a new VM by the import method is somewhat disappointing because you only have the option of importing from a Xen VM exported image. To be a platform that companies switch to, XenServer needs the ability to directly import virtual machines from VMware.


The greatest advantage is that XenServer installed perfectly on my test system — a feat still unaccomplished by VMware ESX and ESXi on the same hardware. That XenServer supports IDE and SATA drives is a huge advantage over VMware which only supports SCSI disks. VMware’s hardware limitations and significant price differential give XenServer a huge boost in the development and corporate sectors.

Like most of its competitor products, XenCenter is very easy to use. Creating VMs from templates or ISO images is a snap. Creating and working with Resource Pools is also very simple. If you’ve worked with VMware’s Virtual Center, you’ll appreciate XenCenter’s speed and simplicity. In a side-by-side comparison of setup and use, XenCenter and XenServer

Does XenServer 5 pass the “first impression” test? Yes. It offers speed, flexibility, scalability, ease of use, and a price that will make your accountant grin. XenServer 5 is a success from download to deployment and a win for Citrix and users alike. There’s much to like about XenServer 5 and very little to dislike. An enterprise-level product built by one of the world’s leading technology companies that’s also free — what’s not to love?

Comments on "XenServer 5: First Impressions"


VMware’s significant price differential?

ESXi = free
XenServer = free

XenServer Enterprise Edition $2200 annual license
VMware Infrastructure Foundations $2,195.00 2year platinum support, 2 physical processors

XenServer Standard Edition $660 annual license
VMware ESXi 3.5 for 2 Processors + Platinum (24×7) 1 Year Support

VMware Infrastructure Foundation Acceleration Kit for 6 Processors $3,744 1year platinum support (includes 3 of the Infa Foundations + VMware vCenter Server Foundation)

VMware ESX Starter Kit – manage 3 ESXi servers $995

XenServer can use SATA & IDE disks, potentially saving money
VMware uses memory a little better, potentially saving money

Right now, the differentiators are features and technology, not price. XenServer has a lot of functionality in the base product that are part of other products on VMware. VMWare can do things that XenServer cannot – yet.

For an enterprise customer, VMware’s features are probably worth the cost, and we appreciate Citrix forcing them to keep their prices low :-) For a small business, either will require significant effort to build and maintain a small (5 server) farm. For the enthusiast or developer – Xen is open, VMWare is easy (run on a host OS).


XenServer windows management application is thumbs down for 2 reasons:

1) Remove server console which uses VNC doesn’t run remotely over the internet. You must be in the same subnet.

2) There is no linux version available which many system admins prefer to use, you will have to stick to the command console.

VMWare ESXi lacks support for basic hardware such as QLogic Fiberchannel HBAs, so connection to our SAN was not possible! XenServer5 handled these without any problem.

Something to say about the support:

Citrix installation support – 3 days no answer
VMWare support – 1 day got an answer

And the license costs with VMWare are significantly higher as your virtualization solution grows in size, referring in particular to live migration and “enterprise” tools.



Xen Server Enterprise Edition is now free. No costs. See last week’s column entry Strange Bedfellows: Citrix, (Free) Xen & Microsoft. ESXi is not comparable to XenServer 5. VMware will tell you this too. It is a step up from VMware Server but still not ESX. Don’t kid yourself.

XenServer has several advantages over VMware besides price but that isn’t anything to sneeze at, to be sure. One is that management is done via XenCenter…a small Windows app. No Virtual Center server needed and it isn’t, thank goodness, Java-based.

VMware doesn’t use memory more efficiently…less so in fact–ever hear of “ballooning?” That is not efficient, it is unsmart. XenServer is also has far better disk I/O…that’s why all the cloud vendors use it. VMware’s days, as the dominant force in this market, are numbered.


I read this review with interest, having tried Xen on RHES5 and been disappointed it didn’t support foreign guest O/S’s.

Not being already familiar with XenCenter, I have to glean that the host computer is Windows and the guest is Linux? Or is XenServer the bare metal host and XenCenter runs on a client or hosted O/S Windows? The article is not clear. Since this is an open source oriented magazine, I was wondering if the opposite setup is possible, can one have a Linux server and a Windows host? If so, why was this not the First impressions test setup?


Have you looked at Virtual Iron?


Don’t kid yourself.
I’m not, that’s why I tried to make an apples to apples comparison, and even pointed out that the free XenCenter does more than free ESXi.

VMWare, in our experience, does use memory much more efficiently. On web and applications servers, we overcommit memory by 100% without any performance impact. We are rolling out Exchange at 100% overcommit. On file and print, it is 200%. As we get more experience, we’ll be upping this. Many of our web apps are bursty – very busy at the end of the month, quarter, and year, less so other times. With similar workloads (Xenserver4, to be sure) we saw performance impact at 50% (allocate 1.5xRAM).

Yes, I have heard of ballooning. Xen 4 had it, but it was not supported by Citrix. It was tried in 4.1 beta and dropped. It was promised in 5, then dropped. By Citrix’ own admission, Xen ballooning is not ready for production. VMWare has it, as well as page sharing across VMs. Citrix claims there is a performance hit for page sharing, but with modern (multicore, with Virt. support) cpus, we haven’t seen it. On VMware, it just works. The only thing keeping us from overcommitting more is a lack of experience – we’ve only got about 18 months of data to analyze.

All the cloud vendors use Xen (and probably not XenCenter) because it is free, and they’re looking at provisioning hundreds or thousands of servers. Like HPC, the lack of a toolset to do provisioning and monitoring is a minor problem – you use open source or write custom products. (As an aside, does Xen have the equivalent of VMotion – that would be a great enabling technology for cloud.)

I don’t think we’re as far apart as you seem to. I’m just trying to make the point that for enterprise customers, paying extra for VMware’s suite makes sense, because it allows you to do things the other products cannot, or allows you to do easily or cheaply things that are difficult on other products.

For SMB or developers, XenCenter might well be the right choice. For us, it will be at least 1-2 years before other vendors begin to offer the features we need – and by then, we will likely be using features and products that only exist on VMWare. For example, Site Recovery Manager, which fails applications (not just servers) to different data centers. You have to have synchronized storage between the datacenters (big $$), but it solves a lot of DR problems.

Regards -


How does Xen Server compare to Xen Source at http://xen.org
I never found how the two are related.


Xen rpm and kernel are not very impressive. In fact, if that were the only option for using Xen, I wouldn’t. The XenServer product is a true hypervisor and VM performance is very impressive. I think you’ll see it differently if you check it out. Let me know after you do, I’d love to know how it goes.



You’re right, sorry. I must have read your post and answered in haste. I just don’t like the idea of overcommitting of memory. I’m glad you’ve had good luck with it.


Ok, having done virt (working for an integrator/consultancy) for a long long time I thought i’d add my own personal experiences.

First, imho free ESXi vs free XenSever is a draw. You get more with XenServer but the big one is live motion – that is a pretty big piece of useful functionality right there in the commercial world – its almost a “xenserver wins” point. The other thing that is a win for Xen is

Now, personally, i’ve mostly used Xen (enterprise) as an embedded product not as a native OS (thought 5 made me run out and throw it on a few servers just to see it go).

By the way, the difference between ESX and ESXi (functionally) is zero in terms of virtualisation (in fact, ESXi will run – even if its not supported – on almost anything and will support hardware ESX will not, ESX just gives you a console). v4 for VMWare was going to see ESX go away but it was kept for vendors who aren’t ready to integrate ESXi yet.

There are a couple of big wins for ESX(i) though – for eg, it supports almost anything as a virtual OS (you’d be supprised how often I still run into machines running NT4). ESX(i) does tend to be generally more flexible with guests (and this can become really important in alot of situations).

ESXi can also be imaged straight onto a flash drive, plugged in, and away you go (i had alot of fun trying to get xen 5 to boot off a usb drive – installed straight onto it but took messing with the initrd in order to get it to boot).

ESX does have a web gui (not great, but not horrible either) and for a desktop-linux user this can be quite handy. I like the command line, but for something complex learning every intricacy of its execution can be an annoyance (ok, so esxi does not have a web gui as complete as esx). I’ve had very very limited success in running either xencenter or the virtual infrastructure client in either wine or mono (both are .net btw – not java).

When it comes to “paid for everything” versions of the software, i still find that its tending towards vmware though. P2V and failing hardware seems to be much better dealt with in ESX, but not having a dedicated box (virtual or otherwise) running the virtual infrastructure service (a mostly-j2ee app running on windows? this will apparently become a virtual appliance running linux in v4, maybe) is a plus. VMWare though do have quite a plethora of management tools (as well as 3rd party tools) that add to its ease of use. I remember when Xen stopped being able to boot Acronis universal restore – that was quite a major annoyance.

I will say that Xen appears to be slightly better at running VM’s, they just seem to perform a little better. But ESXi boots into around 80m of memory vs XenServers 400 or so.

Personally i think one day not too far in the future people wont care what hypervisor it is because they’ll be managing it from an application some new vendor will push out that can deal with any hypervisor (i.e. hypervisors will become an absolute commodity). I mean, lets face it we already pick our hypervisors mostly based on what the management tools do – which for me means “if your gui would work in linux, you’d make me alot happier!” (note, i am a minority and am not really that serious ;)).

When it comes to VMWare’s days being numbered, I would be more afraid of what hyperv will become rather then xen, its just a personal opinion but MS certainly aren’t sitting still with that.


There are a couple of big wins for ESX(i) though – for eg, it supports almost anything as a virtual OS (you’d be supprised how often I still run into machines running NT4). ESX(i) does tend to be generally more flexible with guests (and this can become really important in alot of situations).


The bane of our existence is applications that are too important to kill, but too expensive to fix. Little department-level crapplets doing one very specific thing, but the guy who wrote them left, or the source code got lost, or … There’s always money to replace them, in next year’s budget, and it always gets cut.

When the hardware they’re running on dies (for purchased servers) or comes off lease, it’s great to be able to spin up a VM and have it keep on running – with no OS or hw changes usually. Ever seen what a hw vendor charges for monthly support on a 5 year old box? With leases, it’s not uncommon for the owner to allow you to continue using the box for a couple of months – at the same lease payment, which is usually about what you’d pay for a brand new box. You can save a lot by replacing 4-5 old servers with one high end virtualization host – and vms 5 – 20 are just icing on the cake.

Best –


Guys, thanks for your comments. I haven’t had a chance to play with Citrix’s XenServer, however I am not that big a fan of Xen on Linux. I know it has the potential to run VMs with a little less overhead, but VMwares networking features are just far superior, and easier to set up. Virtual Box isn’t to bad either, but it doesn’t scale well and tends to act flaky when running a certain amount of VMs, and you have to know a bit about bridging using brctl in order to make the VMs visible from outside the host.

Another bit I just read today in Information Week is that Redhat is dropping it’s Xen support in favor of it’s own KVM. Now they will promise to support it for aorund 7 years, but how do you like them apples?




“VMWare ESXi lacks support for basic hardware such as QLogic Fiberchannel HBAs, so connection to our SAN was not possible! XenServer5 handled these without any problem.”

That is completely wrong. ESXi and standard ESX both support most, if not all, of Qlogic’s FC HBAs (in addition to Emulex and OEM versions of both). That’s all I use and just about all my clients use. Not sure where you got your information from. If you took the time to look at the ESX I/O HCL you’d see the ton of mass storage adapters it supports, including, of course, Qlogic.

Regarding IDE and SATA disks, I see even some on this forum talk about that being an advantage for Xen (or even Hyper-V). Look, you don’t run enterprise applications and systems on ATA technology, serial or parallel. More and more of my clients are now going with embedded ESXi (keep in mind that there is no functional difference between ESXi and ESX-one has RHEL as its booting OS and the other bootstraps via embedded busybox Linux and loads the vmkernel from there-but that’s the only difference). So with the embedded hypervisor (AND Qlogic’s HBAs!!) there’s no need for local disks and even if there was, many are starting to look into solid state drives, like what is available on HP’s 495c blades. Keep ATA technologies for low tier backups of marginally important data, CD/DVD-ROMs, and desktop PCs-but keep it out of the data center.


khess: Xen rpm and kernel are not very impressive. In fact, if that were the only option for using Xen, I wouldn’t. The XenServer product is a true hypervisor and VM performance is very impressive. I think you’ll see it differently if you check it out. Let me know after you do, I’d love to know how it goes.

Xen Source and XenServer use the same sources. IOW, the Xen that you load via the Linux distro packages or from source is the same Xen hypervisor as you get with XenServer.

The only differences between the two is what is loaded on top of the hypervisor. XenServer gives you nice management tools, whereas Xen from source leaves it to you to provide the management tools.

There’s very little you can’t do with regular Xen that you can with XenServer.


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