Tips for virtual desktop performances

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In my last blog entry I wrote the following statement:

“Always be sure to consider any user objections before deploying desktop virtualization and thin client technology.”

One of the main objections is loss of performance.

Migrating physical to virtual desktops is, very often, a good time to set up new versions of applications but new versions always require more resources.

Simple Internet searches about virtual desktop sizing on any hypervisor always give the same advice about the following four resources:

  • CPU sizing:
    Depending on the application, you can deploy from 6 to 9 virtual desktops by core.
  • Memory sizing:
    Minimum size is 1 GB for Windows XP and 2 GB for Windows 7.
  • Storage sizing:
    The sizing of your storage needs is all about performance and has nothing to do with storage capacity. Storage is calculated by the amount of I/O operations per second (IOPS) needed. Standard value is from 5 to 20 IOPS, depending on applications and operating system.
  • Network sizing:
    This sizing is the bandwidth required between a data center and the user’s desktop, which could be a workstation, thin client or any device, depending on the protocol used, and application graphics resolution.

The following table summarizes the best practices for the standard components.

Component Best practice
Memory XP:  1 GB

Windows 7:  2GB

Disk space XP:  10 GB

Windows 7:  20 GB

Processor 1 vCPU
VM / LUN 15 – 40 depending on user-type (task worker, knowledge worker)
Bandwidth From 20 Kbps to 100 Kbps or more, depending on the protocol used and applications


Best practices don’t mean best performances.

The virtual desktop experience must be equally as good as the physical desktop experience for the user.

During my last desktop virtualization project, I was asked to give special attention to user experience in terms of performance and visual rendering. I did some testing with pilot users and it was a user-experience disaster.

After testing, I modified virtual desktop settings with the following values:

Component Best practice
Memory XP:  2 GB

Windows 7:  3GB

Remember that the memory swap process decreases overall performances.

Processor 2 vCPU

The visual effect on application launch is amazing.


Avoid the following issues:

  • Memory over commitment
  • Memory ballooning feature. Use this carefully (if available with your hypervisor).
  • More than 40 virtual desktops on a server with four quad core processors

Hypervisor global memory must be equal to the number of desktops times the desktop memory plus the hypervisor base requirement. (Add all memory needed by each component.)

First, tests must be done on the local network to avoid external network impact. By being on the local network, we get the real performance without WAN problems.

Remember that every project is different and the pilot phase is very important.

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