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Hyper-V Server is Finally Here – But What Exactly Is It?


First, Thank-you for the Feedback

I wanted to quickly say thanks to everyone who provided feedback on our most recent post comparing the installation and configuration of VMware ESXi versus Windows Server Hyper-V with Server Core — Microsoft’s recommended deployment option.  You may not agree with all of the conclusions we presented, but we just couldn’t let Microsoft Exec Bob Muglia go unchallenged in claiming that Hyper-V is simply “The Windows You Know” and therefore an easier product to use than ESXi – it isn’t.  But thank-you, as many of you had very insightful (inciteful?) comments and we got some good, healthy debate going. For a pretty fair Microsoft response, please refer to James O’Neil’s blog .

But “Apples to Oranges”??  They’re Both Hypervisors!

But there was one piece of feedback, stated in comments by a number of Microsoft employees readers, that puzzled me. Some people cried foul because they saw our evaluation of Hyper-V with Server Core and ESXi as somehow comparing apples to oranges – I guess that was because Windows Server Hyper-V with Server Core requires a full instance of a general purpose operating system as its parent partition and ESXi does not. The comments/bloggers suggested that a more fair comparison would be ESXi vs. Hyper-V Server 2008, since Hyper-V Server is supposedly Microsoft’s ‘thin’ hypervisor that doesn’t require Windows Server OS in the parent partition – as reported by Microsoft here.  (Note: the MSFT blog linked there incorrectly states that ESXi has a Linux parent partition. That is untrue, ESXi has no parent partition.)

Well, regarding “Apples to Oranges” I am not going to dwell too much on that one, because in my opinion, ESXi and Hyper-V (all configurations) are both Hypervisors and are both aiming to serve the same purpose within a customer’s datacenter, so therefore the comparison is valid.  And, to support that notion, Microsoft compares all versions of Hyper-V to ESX/ESXi in every one of its virtualization presentations, so I think they’re in agreement with us that it is a fair comparison.  However, given that, if you want us to compare ESXi to Hyper-V Server, sure, now that the product is finally available, we can talk about that one too.

Hyper-V Server – Initial Thoughts

Ever since Microsoft first announced Hyper-V Server, almost a year ago, we’ve been speculating as to what it would look like.  It was billed as “standalone”, but until right before its release, Microsoft provided no technical details, so we were all left in the dark.   Existing Hyper-V versions were wholly dependent on Windows Server, so how “thin”, how “standalone” could it really be?

(Note: I am actually thinking that, at the time of Hyper-V server’s announcement, Microsoft itself didn’t know what the Hyper-V Server 2008 architecture would look like…)

Well, now that Hyper-V Server 2008 has finally been released – with very little fanfare considering its initial push from Microsoft – we were able to perform a preliminary evaluation.   There were two things we were initially interested in: 1) How the Hyper-V Server deployment/configuration processes compare to ESXi – gotta answer our critics, and 2) How Hyper-V Server architecture compares to ESXi – is it a more “apples to apples” comparison, or does Hyper-V Server contain Windows Server OS and is it therefore subject to all the patches, updates, vulnerabilities of the other configurations of Hyper-V?

We’ll save tackling the first issue — comparing the install/configure processes – for another blog post.  While our initial eval tells me that the install/config process hasn’t improved with Hyper-V Server, it will still take a little time to undertake a complete analysis.  But the second item – understanding what components of Windows Server the Hyper-V Server actually contains, how the architecture compares to ESXi, and what the benefits of Hyper-V Server actually are – we can start that discussion here.

Hyper-V Server is not “Windows-less” but is merely “Windows License-less”

Our initial finding is that Hyper-V Server is not “thin”; Hyper-V Server is still ultimately Windows.  Hyper-V Server appears for the most part to be just Windows Server Hyper-V with Server Core where all other Server Core roles (except Hyper-V) have been disabled. Hyper-V Server has practically the same footprint as Windows Server Hyper-V with Server Core and is subject to the same patches, updates, attacks. It also appears to have the same restricting, indirect Windows-based driver model. In fact, it seems that the only advantage of Hyper-V Server is that one doesn’t have to buy a Windows Server license in order to deploy it – that’s it.   Hyper-V Server is not “Windows-less”, but just “Windows License-less.”

Hyper-V Server also has some significant limitations that it seems to have inherited from the Standard Edition of Windows Server 2008. It can only support a maximum of 4 sockets per host, 32GB of physical memory per host, 31GB of virtual memory per VM, and requires a rip and replace upgrade to support features like Microsoft Clustering and Quick Migration. So it seems that Hyper-V Server is more of a starter kit, meant only for very basic use cases. In comparison, ESXi is a fully functional, production ready, enterprise offering. Actually, as 1) Both ESXi and Hyper-V Server are free and 2)Only free ESXi can easily be upgraded via license key to a production solution, why would anyone ever use Hyper-V Server? What’s the advantage?


Virtualization Needs

Microsoft Hyper-V Server 2008

VMware ESXi
Free Hypervisor

Small Disk Footprint

No – 2500MB

Yes – 32MB

Large Host Memory Support

No – 32GB

Yes – 256GB

Maximum Physical CPUs



Maximum VM Memory



Supported Guest OSs



Memory Over-Commitment






Clustered File System


Yes – VMFS

Simple Upgrade Path


Yes, to full VI3 versions

Hyper-V Server – An Overview of Our Installation Experience

For proof points supporting our above conclusions, following is a blow-by blow of Michael Hong’s experience installing Hyper-V Server:

I got my 936MB iso of Hyper-V Server downloaded. I burned it onto a CD and popped it into my brand new HP DL 360 and fired it up. After doing some recommended BIOS configurations and rebooting, I’m watching the boot sequence and getting a feeling of déjà vu. Did I just put in the wrong DVD? Because I swear this looks exactly like a full Windows Server 2008 or even a Server Core installation.


Wait…did that just say, “Installing Windows?” I thought this was Hyper-V Server that wasn’t supposed to be Windows! At this point I’m thinking, “Hey, maybe that’s not too bad. I can get a free copy of Windows without having to deal with any of their licensing nightmares.” Well let’s wait and see before I get too excited…

Hyper-V Server Disk Footprint is Similar to Hyper-V Server Core!

Okay, so after THREE more reboots I’m finally able to log in and start looking around. The first thing I check is Hyper-V Server’s disk footprint. After all, Microsoft states that one of its only three key benefits is a “small footprint.” So how “small” is it really? After plotting the numbers into my trusty byte convertor, Hyper-V Server is coming in around 2.5GB! (pagefile not included in size) WOW, that’s only a hundred megabytes less than a full-blown Windows Server Core installation! Perhaps it really just is a Windows Server Core Standard edition with one role enabled. Anyone else have any thoughts on this?


Also notice the number of files and directories. My basic install of Windows Server Core with Hyper-V enabled has:


In this install of Hyper-V Server there is actually more files and directories:


Next, let’s take a look at patching. Option number 5 in the dos-like Hyper-V Configuration menu shows an option for enabling Windows Update. Once set to automatic, it scanned for applicable patches. I didn’t expect to see any new patches since Hyper-V Server was just released yesterday. Any new patches would probably arrive next patch Tuesday right? And since this is supposed to be a light, secure hypervisor, it probably wouldn’t need as many patches as a full blown OS right? The results may surprise you:


13 applicable patches, including 2 for Internet Explorer 7? This is looking more and more like the “Windows I Know.” What in Hyper-V Server actually relies on IE7? Hyper-V Server looks like it’s a full blown Windows OS. If that’s the case, I’m sure hackers will have a field day copying over few additional files and turning it into a full working copy of Windows Server Core.

Some other things to keep in mind:

· Server Core and Hyper-V Server have the same directory structures

· Server Core and Hyper-V Server have the same command line toolset

· Server Core Standard and Hyper-V both have the same 32GB of physical memory limit and up to 4 processors

· Server Core and Hyper-V Server have the same parent partition driver model

Is Hyper-V Server really Windows Server Core Standard with only the Hyper-V role enabled? If so, will it be vulnerable to the same threats as Windows? Those 13 patches are just the starting point. What about viruses? Windows Server Core is exposed to viruses and as a result, there are anti-virus products out there today that are certified on Server Core. What about the size of Hyper-V Server’s footprint? Being only 100MB smaller than Server Core still shows it still has a very large attack surface as compared to VMware ESXi.

In Sum

We feel that, in contrast to how it is being marketed, Hyper-V Server 2008 is not “standalone”, “thin”, or  Operating System agnostic in the same manner as ESXi. Hyper-V Server is still very dependent on and subject to the limitations of Windows and therefore should not be considered an equal to ESXi.   Also, given Hyper-V Server’s restrictions and lack of upgrade path, and given that ESXI is also free and has a simple upgrade path, I question what the viable use cases for Hyper-V Server really are. Give it a try yourself and let us know what you think.  Better yet, download our free VMware ESXi and let us know how you feel it compares to Hyper-V Server.

Stay tuned for our comparison of the deployment and configuration processes for ESXi and Hyper-V Server.

12 thoughts on “Hyper-V Server is Finally Here – But What Exactly Is It?

  1. John h

    nice writeup – I enjoy reading your blog as while obviously pro-VMware, your arguments are usually based in fact rather than just marketing hyperbole. I also don’t see a real use case for hyperV Server aside from potentially offering someone who doesn’t have any windows server 2008 in their environment a chance to test hyper-v side by side with esxi – yes a small potential market

  2. James Russell

    If ESXi doesn’t have a parent partition/console OS/whatever, what do you consider the instance of BusyBox with which users interact? Are you asserting it’s not a parent partition because it runs directly within the vmkernel rather than in a guest-level world? It’s still a non-VMkernel piece of software glued running on the system in order to manage it.

  3. Tim Stephan

    James – thanks for the comment – just to clarify, Busybox is just a shell plus set of utilities that runs on ESXi. It has nothing to do with the functionality of the box. It is only useful for fixing problems, namely, modifying or deleting system files and stopping or restarting system processes. It is not needed to manage the box. If desired, BusyBox can be disabled with no impact to performance.
    The point regarding the management partition that I was making in regards to ESXi, is that Hyper-V (Windows) and Xen (Linux) still require a substantial instance of a general purpose operating system in order to function. This “Parent Partition” for Hyper-V or “Dom0” for Xen includes a whole lot of code that has nothing to do with virtualization but negatively impacts the performance and reliability of your virtualization infrastructure, as it has to be patched and updated – often requiring a reboot of virtual machines on the host – and introduces security vulnerabilities into your environment. ESXi is stripped down to only the essential code required for virtualization – it carries none of the dead weight of other hypervisors, meaning a more secure environment with fewer reboots and patches.

  4. Gavin

    The IE Patches are required as the product activiation is handled by some IE components … so obviously they should be patched accordingly.

  5. guest

    ESXi use a linux parent partition too. This partition is smaller becaouse it uses a reduced busylinux instead of rhel. Without this partition you cant boot the vmkernel or run vpxa agent… how do you manage esxi without the root partition? how do you disable it? or how do you run vmkernel without linux partition?

  6. Kenon Owens

    Thank you Gavin for the response. This “linux parent partition” is not a partition like Dom0, or the Parent Partition for Hyper-V.
    ESXi has a special troubleshooting interface call Tech Support Mode (http://kb.vmware.com/kb/1003677). This interface should only be used when troubleshooting issues with Technical Support. This shell + utilities is NOT necessary to be enabled for ESXi to function. As stated in the KB article:
    Administrators can disable or re-enable Tech Support Mode on each host by modifying advanced configuration parameters. Each time the setting for supporting Tech Support Mode is changed, you must reboot the host before the setting takes effect.
    To disable Tech Support Mode:
    1. Connect VMware Infrastructure Client (VI Client) to an ESXi host or a VirtualCenter Server.
    2. Browse to a host in the inventory list.
    3. Click the Configuration tab.
    4. Click the Advanced Settings link.
    5. Click “VMkernel” in the left-hand side pane.
    6. In the list of parameters, deselect VMkernel.Boot.techSupportMode.
    7. Restart the ESXi host. Before restarting the host, you should shut down virtual machines on that host or migrate them to another host using VMotion or cold migration.
    Since you can run ESXi with Tech Support Mode disabled, you can see that ESXi doesn’t rely on this, and it is nothing like the Console OS of VMware ESX 3.
    To see what it looks like and to understand the difference, check out my blog at:

  7. guest

    I know SC linux partition is not like dom0. But if you disable SC where do you run vpxa agent, tomcat for webacess, iscsi auth, parport, serialport redirection, and so on??
    And how do you book vmkernel without linux partition?
    I think that what you are talking is about hidding this partition for the final user.
    Do you have any technical documentation about it? As is a question I argue usually with customers.

  8. Mike DIPetrillo

    I think you’re confusing 2 different architectures of ESX. There’s ESX (I call it classic) that has a Service Console that runs RHEL3. In versions prior to ESX 3 the Service Console acted as sort of a bootstrap (ala old NetWare days) to boot vmkernel. Once vmkernel was booted then the Service Console became a VM that was there for management agents and such.
    With ESXi there is no Service Console. It’s not hidden or anything – it’s not there at all. There is a Tech Support Mode as Kenon points out but even that you can disable. Tech Support Mode is not needed to run the box.
    Starting with ESX3 (classic or “i”) vmkernel actually boots the box and if you’re running ESX then it loads the Service Console as a VM. The classic version is around while management companies port their applications over to the API set that has been available for the last couple of years.
    So again, the Service Console is not needed to actually run VMs. In Hyper-V or Xen the parent or dom0 partition is needed if you want any I/O to go through the system. That’s the biggest difference.

  9. Lior Ben-Dror

    How about this often-overlooked parameter called performance? I had to set up a lab of 10 physical machines, each of which running around 5 VMs. The default was ESXi, but then we realized that disk I/O maxed out at 10MB/sec. Yes- 10MBytes/sec, no matter what disk was accessed: DAS, NAS, iSCSI – this was the max we got. I approached several other VMWare customers that initially all reacted: “can’t be!” and then tried their own systems, just to get IDENTICAL RESULTS! We called in VMWare consultants; -$2500 but no improvement whatsoever to the poor ESXi performance. We then tried XenExpress. An excellent product which showed us that hypervisors can get to 5x the ESXi I/O performance (which is the native hard drive performance). Unfortunately XenExpress didn’t have the features we needed, so we tried Hyper-V Server. What an amazing product! Forget about the stupid parent partition debate- it’s purely academic. In practice Hyper-V Server is perfect. We then discovered that as MSDN subscribers we can freely install Microosft’s System Center Virtual Machine Manager, which is an amazing management console with lots of features (and actually, we can install as many Win2008 servers as we like WITH the Hyper-V role- this enabled features like cloning and vMotion). Now we are set with a perfect lab that performs at max I/O speeds. The days of VMWare are over mainly because performance sucks and VMWare doesn’t know how to fix it. After we switched to Hyper-V we discovered numerous other benefits, but the key decision factor was performance. If it was good (not even excellent) we wouldn’t take a look at Hyper-V.

  10. Mike DIPetrillo

    Not really sure what you did to test performance but I think you might have done something wrong on the ESXi side. Here are three public examples showing tests that demonstrate line speed throughput for ESX/ESXi (they have the same architecture and code for I/O):
    Storage Protocol Performance (shows 1 Gb for NIC and 2 Gb for Fiber)
    100,000 IOPs (at 8k blocks that’s 800 Mb/s)
    16,000 Exchange Mailboxes (8,000 IOPs which meant 64 Mb/s)
    All of these show conclusively that something went wrong in your tests. Not sure what. If you’d like to share the methodology then we’ll be happy to see where things went south.

  11. James

    Perhaps Hyper-V is suitable for use on a server equipped with a SATA RAID controller not supported by ESXi,
    but that does have a Windows driver floppy available?
    In this case, ESXi isn’t an option, because it won’t work on the hardware.
    Linux-based solutions like Xen and Hyper-V become the only option in these cases.
    I say this, because I have to work with a lot of hardware that ESXi won’t even recognize — so we’re stuck with solutions like Xen, unless/until ESXi can ever finally work on that equipment, or provide a public driver development kit or other method, for me to write or port/compile drivers that will work with it.

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