Differencing Disk

Definition of Differencing Disk

A differencing disk is a virtual hard disk (VHD) used by virtualization software. It acts as a child disk to a parent disk, storing only the modifications made to the parent disk rather than duplicating the entire disk. This approach enables efficient use of storage space and faster virtual machine setup by reducing duplication and consolidating changes.


The phonetic transcription of the keyword ‘Differencing Disk’ is:/ˈdɪfərənsɪŋ dɪsk/Here’s a breakdown of the pronunciation:- “Differencing”: /ˈdɪfərənsɪŋ/ (DIF-uh-ruhn-sing)- “Disk”: /dɪsk/ (DISK)

Key Takeaways

  1. Differencing disks are a type of virtual hard disk (VHD) used primarily for reducing storage requirements and improving performance, by storing changes from a parent VHD, while leaving the parent unchanged.
  2. They are frequently used in scenarios such as operating system updates, software installations or testing configurations, where the base VHD can be quickly rolled back to its original state when needed.
  3. Although they provide storage efficiency and easy rollbacks, managing multiple differencing disks can become complex, as they form a dependency chain and require careful handling to avoid data loss or corruption.

Importance of Differencing Disk

Differencing Disk is an important technology term because it plays a crucial role in virtualization environments, efficiently utilizing system resources, and simplifying management tasks.

It is a virtual hard disk (VHD) that stores modifications to the virtual machine parent disk, enabling multiple virtual machines to share a single baseline operating system (OS) image without affecting the parent disk.

This not only reduces the storage space needed but also streamlines the process of updating, patching, and deploying new virtual machines.

By using differencing disks in virtualization, IT administrators save time, enhance performance, and optimize disk management, ultimately contributing to a more robust and efficient virtual environment.


Differencing Disks serve a vital purpose in the realm of virtualization, aiding in efficient management of virtual machines (VMs) and conserving valuable system resources. These disks operate by deriving their data from parent virtual hard disks (VHDs), which store the base version of an operating system (OS) or application files. This approach allows the differencing disk to store only incremental changes that are made to the parent disk, thus reducing the overall storage footprint.

By doing so, multiple VMs can run on a single host system without having to duplicate the entire base data for each instance. Consequently, this results in significant savings in terms of space, time, and administrative effort, facilitating quicker backups, faster provisioning of VMs, and better overall performance. In addition to resource conservation, differencing disks prove invaluable in testing scenarios where a stable and consistent environment is required.

Developers and IT administrators often create sandboxed environments using parent VHDs, allowing them to conduct isolated testing and make modifications without affecting the original base disk. As these differencing disks only keep modified data, they enable users to roll back to the original state if an error occurs or undesirable changes are made. This functionality also makes it possible to test multiple configurations and perform comparative analysis by creating separate differencing disks for each test scenario.

In summary, differencing disks not only serve as an effective means for managing storage resources but also equip users with a safe and flexible workspace to troubleshoot and optimize their virtual environments.

Examples of Differencing Disk

A Differencing Disk is a virtual hard disk (VHD) used in virtualization environments to optimize storage and improve performance. It operates by capturing changes from a parent VHD, allowing multiple virtual machines to share the same base image while storing the changes made to each instance separately. Here are three real-world examples of Differencing Disk technology:

Microsoft Hyper-V Virtualization: Hyper-V is a native hypervisor offered by Microsoft that allows multiple virtual machines to run on a single physical server. In this environment, differencing disks can be used to save storage space and improve performance. For instance, multiple virtual machines running the same operating system and applications can share a single parent VHD and each VM would have a differencing disk to store custom data and changes specific to itself. This greatly reduces storage need and allows for faster provisioning of new virtual machines.

Educational and Testing Labs: In educational institutions or businesses that need to run multiple instances of software on multiple devices for trainings, testing or development purposes, a differencing disk setup can be particularly useful. By creating a base virtual hard disk (VHD) with all the necessary software and configurations installed, a differencing disk can be created for each user. This way, individual users can make changes and work independently without affecting the original base VHD. When a new session starts, the differencing disks can be reset or deleted, ensuring that each user starts fresh and saving storage space.

Managed Service Providers (MSP) and Data Centers: In a managed service provider or data center setup, virtualization is common for efficient resource management. Differencing disks help in creating virtual machines with shared base images and customized configurations for individual clients. This streamlines the deployment process and reduces storage requirements. Additionally, it allows the service provider to easily deploy updates and patches to the base VHD, ensuring all customer virtual machines are up to date, while still retaining their customizations.

Differencing Disk FAQ

What is a Differencing Disk?

A differencing disk is a type of virtual hard disk (VHD) that is associated with another VHD, called the parent disk. The differencing disk stores the changes made to the parent disk, allowing the parent disk to remain unchanged and the differencing disk to contain only the data that has been modified.

What are the advantages of using a Differencing Disk?

The main advantages of using a differencing disk include reducing disk space usage, increasing performance in virtual environments, and making it possible to revert virtual machines to previous states easily. Differencing disks can also help in protecting the parent disk from unwanted changes or in creating multiple virtual machines with a shared base image but distinct customizations.

How to create a Differencing Disk in a common virtualization platform?

In a common virtualization platform like Microsoft Hyper-V, creating a differencing disk involves the following steps:
1. Open Hyper-V Manager.
2. In the Actions pane, click on “New” and then “Hard Disk”.
3. In the New Virtual Hard Disk Wizard, select “Differencing” as the disk type and click “Next”.
4. Specify a name and location for the differencing disk.
5. Choose the parent disk for the differencing disk.

Can a Differencing Disk be merged back into its parent disk?

Yes, a differencing disk can be merged back into its parent disk, combining the changes stored in the differencing disk with the parent disk to create a single updated virtual hard disk. This can be useful in cases where the differencing disk needs to be removed, or the changes made need to be applied permanently to the parent disk.

What are the potential limitations or issues of using Differencing Disks?

While differencing disks offer several advantages, they also come with some limitations or issues. These include potential performance degradation, increased storage management complexity, and the reliance on parent disks. If the parent disk is deleted or corrupted, the differencing disk cannot function correctly. Additionally, as changes accumulate within the differencing disk, it may grow large in size, offsetting the initial disk space savings.

Related Technology Terms

  • Base Disk
  • Virtual Hard Disk (VHD)
  • Snapshot
  • Dynamic Disk
  • Chain of Differencing Disks

Sources for More Information


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