Hyper-V Dynamic VHDs Test

A VHD (Virtual Hard Disk) is a dynamically expanding disk on the Hyper-V server, which is initially at a few kilobytes and expands when the VMs need additional storage space. The VHDs can only grow as the VMs add data, however, to the size limit which is designated in the setup wizard. The VHDs enable administrators to create, configure, and boot physical computers without a virtual machine or hypervisor. This functionality simplifies image management because it allows to:

  • Standardize the image format and toolsets in the organization.
  • Reduce the number of images to catalog and support.
  • Enable increased server utilization to conserve energy.

If one/more VMs on the Hyper-V host utilize more dynamic memory resources (from the VHDs) than they are supposed to use, then, other VMs on the host may not have sufficient memory resources resulting in serious memory contention. To avoid memory resource contention among the VMs that use the VHDs, it is necessary to continuously track the dynamic memory allocated to the VMs from time-to-time. The Hyper-V Dynamic VHDs test helps administrators in this regard!

This test auto-discovers the VHDs of the target Microsfot Hyper-V server and reports the memory utilization of each VHD. Using this test, administrators can detect the VHD that is hogged continuously for memory resources.

Target of the test : A Microsoft Hyper-V VDI server

Agent executing the test : An internal agent

Output of the test : One set of results for each VHD attached to the Microsoft Hyper-V VDI server being monitored.

Configurable parameters for the test
  1. Test period - How often should the test be executed.
  2. Host - The host for which the test is to be configured.
  3. Port - Refers to the port at which the specified host listens to.
Measurements reported by the test
Measurement Description Measurement Unit Interpretation

Total size

Indicates the total capacity of this VHD.



Used size

Indicates the amount of memory that is utilized by the VMs from this VHD.


By comparing the value of this measure across the VHDs, you will be able to identify the VHD that is being utilized at all times.

If the value of this measure is close to the Total size measure, then, there may not be adequate memory resources for all the VMs associated with the VHD. This may cause performance bottlenecks in the VMs that are using the VHD.

Free Size

Indicates the amount of memory that is available for use by the VMs in this VHD.


Ideally, the value of this measure should be high.

Percent usage

Indicates the percentage of memory utilized on this VHD by the VMs.


Ideally, the value of this measure should be low.

If the value of this measure is nearing 100%, then, there may be a performance bottleneck in the VMs that are using the VHD due to memory resource contention.