I have tried two ways of working with my 30-40 GB dynamically expanding VHD which contains a Windows 2012 Server install:

  1. VHD mounted as boot volume
  2. Windows 7 as host os with VirtualBox as virtualization layer

It appears that the second way performs much slower in terms of virtual harddisk activity! Is there a way to optimize this while keeping Windows 7 as the host os?

My machine properties:

  • i7 2,4 Ghz CPU
  • 32 GB internal memory
  • 7200 rpm 500 GB hard drive

Virtual machine properties:

  • 4 CPUs
  • 16 GB internal memory

When you boot into Windows 7 and run a VM with a VHD on the same drive, both OS's are competing for disk activity on the same physical disk.

The best solution is to add another physical HDD, solely for the use of the VM. This way the two OS's arent competing for the same disk's resources. Sencond best, would be to add a new hard disk, and create a VHD on the new physical disk. Alternatively, you could partition the first hard drive and create a second volume for the VM, but the performance increase would be minimal at best, as they are still on the same physical disk.

Also, dynamic hard drives are never recommended, unless you are very short on space. If you are bumping up the disk size constantly, the performance will be severely degraded. If space is not an issue, always use a fixed disk size.

  1. Along with Microsofts recommendation you can try a fixed VHD

    The I/O performance is highest for fixed VHDs because the file is not dynamically expanded.

  2. Have in mind that your first solution using a VHD mounted as boot volume has only a 1-2% decrease in performance

    Microsoft originally set the target of maximum 10% performance loss when Windows 7 is installed inside a VHD compared to a bare metal installation. They have done good work on this part because tests show that this loss is about 1 or 2 %. There is always some noise inside those tests so you can say that it nearly approaches a bare metal installation. My own experiences during the last weeks are the same; you almost never feel you are working inside a VHD.


I would convert to a fixed disk if you hope to have a decent experience. This allocates all the space at once and doesn't 'dynamically expand' at the most inconvenient times (Murphy's law). I used to use those and wondered while imaging them why it would take forever, it's still slightly slow w/ fixed disks but much faster. That's likely a huge bottleneck for you.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.