Not all Virtualization Platforms are the same

21Mar08

There was a discussion today in a peer network of mine about virtualization.  It started out as a request for ballpark pricing on VMWare but turned into a “VMWare is too expensive, use this instead it does everything and is cheaper” discussion.

I am a huge fan of VMWare and since I have first hand knowledge of the subject felt I needed to jump into the mix.  I wasn’t trying to offend anyone or piss anyone off, but wanted to explain things with a little more depth.  Below you can find an exerpt from my response.  I’m interested to see if you agree or not.

Now for the messy part: Why should you (or shouldn’t you) choose VMWare?  I am not claiming to be a virtualization expert by any stretch of the imagination so if something I say is wrong I welcome the corrections.  I do however spend a lot of time with virtualization both via research and by managing an ESX environment for the past two years.  My short comment is:  Leviton and Cisco both make switches, both of which pass packets, but there is a reason the Cisco equivalent costs more.  The same is true with virtualization platforms.  Read on for the long version.

When we were looking at virtualizing our environment a few years back, VMWare stood out as the clear leader.  If I were to start the process today VMWare would still get the top ranking in my book and this is why.

XenServer and Virtual Iron, while they are great options, are not yet on par with VMWare from a features or resource utilization standpoint.  If you are only looking to run a few vm’s on a physical box and you just need a hypervisor with minimal features, then I agree that they are more cost effective options.  If you want to get the most out of your hardware and really utilize the features available in an virtualized environment then I think VMWare is the natural choice.

Virtual Iron is less expensive when you look at it from a licensing per socket standpoint.  They also have some features such as live vm migration, dynamic load balancing, and high availability.  The features are all first generation though, and like a first generation car model, I try to stay away.  As for the utilization, and I will talk more about why later, on equal hardware VMWare will be able to host more vm’s than Virtual Iron.  So when you start looking at cost per vm as opposed to cost per physical CPU it quickly balances out.

Citrix XenServer does not have nearly the features of VMWare such as Dynamic Load Balancing, High Availability, Centralized Backup, Automated Patching, or Integrated DR.  The same holds true here in that you will be able to run more vm’s on equal hardware with VMWare.

So why can you run more vm’s on equal hardware using VMWare?  They have a great feature called transparent memory page sharing, aka memory oversubscription.  VMWare monitors each OS installed on a host and saves only one copy of the common memory page while keeping track of the differences.  This allows you to power on vm’s with more memory allocated to them than the actual physical memory of a host.  Also, windows machines are horrible at letting go of RAM when they are done with it, and VMWare has some very clever ways to re-allocate that memory called ballooning.

As for performance, this is a topic that is debated heavily in the VM community and to be honest I wouldn’t worry about it.  Each company has their strengths and weaknesses in certain performance benchmarks.  VMWare often scores higher in certain benchmarks and Xen chalks it up to VMWare having 10 years experience to optimize and “tweak”.  Xen scores higher in other benchmarks and VMware chalks it up to misconfigurations.  They are all very close however, especially when they are testing with a single vm running on a host.

My last point before I end this novel is something the Xen folk have pointed out in the past and that is VMWare has lots of experience.  They are the Cisco of the VM arena.  They are proven, trusted, and continually innovating.  Hypervisor security has been gaining momentum as the next big threat and it is no surprise that VMWare is already jumping on board by announcing VMSafe and signing partners.  I don’t think you can go wrong with VMWare for the platform you are trusting to run your systems.

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2 Responses to “Not all Virtualization Platforms are the same”

  1. I have come to the same conclusions, but I have taken a different route to them. VMWare’s scalability and portability- from the free offerings through enterprise solutions, make it easy to test and manipulate VMs in a variety of environments. I don’t know of any alternatives which let you move an image between an enterprise box and a Windows PC to a Mac laptop or a Linux system with relative ease- this encourages experimentation, which encourages deployment. Sure you may have to convert the VM, but VMWare Converter is a great tool, and making it free is brilliant marketing. The fact that Converter does clean and easy Physical to Virtual migrations and converts some competing format VMs is great, too.

    I do have some security concerns about things like overlapping memory space allowing data to leak- but they seem to actually be paying attention to security issues so I’m cautiously optimistic about that.

  2. 2 Jack Toering

    The whole idea of virtualization is to run multiple operating systems. VMware works with many operating systems, not just 1 flavor of Linux, and several versions of Windows. I don’t have any reason to run Windows 3.x, 95, 95R2, 98, Millenium, NT4, or Windows 2000. I want more than SUSE. I want FreeBSD etc. The thousands of VMs that vendors use to demonstrate their products are VMware VMs. Since ESXi is free, it means the others would have to pay you money to use them in order for it to be break even.


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