Virtualize XenApp

Here is a pretty common question… I want to virtualize my XenApp servers, how should I carve the physical server up? Should I use a bunch of small VMs or a few massive VMs?

First, you have to look at a few decision points:

  1. OS Scalability: This is more of an issue in Windows 2003.
  2. Operations: More VMs means more to manage, unless you use a single image management solution like Provisioning Services.
  3. Application Requirements: The applications will dictate how many vCPUs and how much RAM you need to fully utilize the VM. Over allocate one and you waste resources. Under allocate one and you waste resources.
  4. Flexibility: How easy is it to migrate active VMs to another server (discussed in the Big or Small VMs for XenApp blog)
  5. Licensing Costs: More VMs means more Microsoft licensing costs. In fact, you might end up moving from Standard to Enterprise or even Data Center.

When we take all of this stuff together, we end up with the following:

Sockets Cores / Socket Hyper-Thread Logical Cores / Socket Logical Cores / Server VM Count vCPU per VM RAM per VM
32-bit Operating Systems  (Windows 2003, Windows 2008)
2 2 No 2 4 2 VMs 2 vCPU 4 GB
2 2 Yes 4 8 2 VMs 4 vCPU 4 GB
2 4 Yes 8 16 4 VMs 4 vCPU 4 GB
4 2 Yes 4 16 4 VMs 4 vCPU 4 GB
4 4 Yes 8 32 8 VMs 4 vCPU 4 GB
64-bit Operating Systems (Windows 2003, Windows 2008, Windows 2008 R2)
2 2 No 2 4 2 VMs 2 vCPU 8 GB
2 2 Yes 4 8 2 VMs 4 vCPU 16 GB
2 4 Yes 8 16 2 VMs 8 vCPU 32 GB
4 2 Yes 4 16 4 VMs 4 vCPU 16 GB
4 4 Yes 8 32 4 VMs 8 vCPU 32 GB

I’ll probably hear a lot of comments for the 64bit systems with using bigger VMs and fewer of them. And those comments would be true. Windows 2008 64bit overcomes many of the bottlenecks we experienced with Windows 2003 32bit. But we are trying to have greater flexibility. We are trying to limit the impact of a VM failure. Bigger VMs means bigger impact if there is a failure.

How closely does your virtualized XenApp environment align? Or how about your plans? Are they retty close?

Daniel – Lead Architect
XenDesktop Design Handbook

4 thoughts on “Virtualize XenApp”

  1. Lets I have 4 physical 2 CPUs/ 6 cores each with 96GB RAM (W2k8 R2 + XENAPP 6). Each server can handle 1000 ICA connections. All 4 are load balanced to accomodate 3000 connections total. Even if I loose one server upon reconnection the rest of the three servers hanlde the load.
    How would it help in going for virtualization on using the same 4 physical server that I have? (most of them prefer vsphere being it has biggest market share eventhough xenserver and hyper -v is avaliable)


  2. Hi Daniel,

    in your table you talk about “logical cores” and assign as much vCPU as there’s logical cores in a physical host, while in the “XenApp Planning Guide: Virtualization best practices” you say “It is advisable not to allocate more vCPU than there are /physical/ cores within the given hardware.”

    In my eyes, this is a contradiction. Or am I getting this wrong?

    Best regards,


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