Virtual Hard Disk (VHD)

What is Virtual Hard Disk (VHD)?

When a virtual file format represents a physical hard drive, it is called a Virtual Hard Disk or VHD. It is typically used to store all the contents of the hard drive of a computer, including the structural and data elements.

Technically, a VHD is a disk image file format with .vhd file extension, which replicates the present hard drive, and is also called the Virtual Machine, sometimes. It is portable and can be kept anywhere reachable by the physical host.

Understanding Virtual Hard Disk (VHD)

What is Virtual Hard Disk

A Virtual Hard Disk is a file format or an application that is specially designed to be used primarily by a Virtual Machine (VM).

Its architecture is pretty much the same as the current physical hard drive of the computer system, including the sectors typically found on it, which include much more than the following:

You can store it anywhere you like, but you must make sure that it is easily accessible to the physical host. For example:

Ideally, storing the VHD in a BitLocker encrypted partition is much better an option because of two specific reasons, such as:

Usually, the Virtual Hard Disks function much like the traditional physical hard disk drives. This is because they have all the capabilities to perform the same functions, which includes but are not limited to the following:

Though a VHD is formed on a physical hard drive, it comes with its own logical distribution.

As a result, these disks can, in turn, host several different virtual hard drives at the same time, though it will primarily depend on their size.

These multiple virtual disks will, however, not interfere with or overwrite the functions of the other VHDs because each of these disks is built as a firmly united drive.

The sizes of these VHDs can be either fixed or flexible, but both will be controlled and managed by either one of the following:

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Created by Connectix for the Connectix Virtual PC software, a Virtual Hard Disk comes with some noteworthy characteristics and features. These features allow doing a lot of different things, such as:

The software was purchased by Microsoft later, on February 19, 2003. They named the product Microsoft Virtual PC to use in the VM applications for the Windows operating systems.

The VHD on a Windows computer appears just like the physical disks when you check it in the Disk Management utility.

The VHD icon will be blue when it is attached and gray when detached, irrespective of the operating system used on the computer, which may be any of the following:

Virtual Hard Disk Types

Ideally, there are three main types of Virtual Hard Disk formats available for use namely, fixed VHD, dynamic VHD, and differencing VHD.

Each of these has different features and capabilities, as explained hereunder:

Fixed Virtual Hard Disk

In this specific VHD format, the disk typically uses a fixed amount of space, just as the name indicates, of the hard disk drive of the host machine.

This specific type of virtual disk has the ability to support much faster data processing speeds and continuous fragmentation.

Dynamic Virtual Hard Disk

In this specific VHD format, once again, just as the name suggests, the disk size is variable.

Typically, the amount of storage space used by this type of disk starts with a bare minimum size, but it gradually grows as and when more and more data is stored on the virtual disk.

The most significant benefit offered by the Dynamic VHD is that it allows much faster allocation of the storage space.

Differencing Virtual Hard Disk

This type of virtual disk is especially useful when it is needed to create a copy of the current hard disk. In this specific format, there are two separate Virtual Hard Disks used.

One of these is called the parent disk, while the other is referred to as its child. The most significant benefit offered by the differencing VHD setup is that it allows making changes to a parent virtual disk without needing to change that disk.

What is a Virtual Hard Disk Used for?

A Virtual Hard Disk is typically used to store all of the contents of a physical hard disk drive in a computer system.

There are also lots of other good reasons to use a Virtual Hard Disk. Some of them are as follows:

How to Open a Virtual Hard Disk File?

In order to open a Virtual Hard Disk file on your Windows computer, you will first have to create it, attach it and then open it. It is not at all difficult when you use the Disk Management utility.

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It will help you to mount the VHD file, copy and even add the files and folders to an image when you need a single folder or a file system image or a VHD file created by Windows backup.

The steps to follow for each of these processes are different and are explained separately in brief for your better understanding.

Creating and opening a VHD

In order to create a Virtual Hard Disk on a computer running on Windows, these are the steps to follow:

Attaching a VHD

In order to make the new VHD partition available for use, you will need to attach it first. The steps to follow for it are:

In order to attach the VHD, here are the steps to follow:

When the VHD is attached to your computer system, it will appear in the Disk Management. However, if it is new, you will have to initialize it to bring it online and open it to use it.

Are Virtual Hard Disk Files Safe?

Well, whether or not the Virtual Hard Disks are safe depends largely on your use.

Usually these files are safe, but they can be dangerous due to several reasons such as combining of the kernel-level file system parsing, allowing the files to arrive at the endpoint or lack of Mark Of The Web (MOTW) tagging to the content that may prevent finding the source of a file from the internet.

There are also a few other instances when the VHD files may prove to be dangerous for a computer system. These are:

It is up to you to make using the VHD files safe. Some of the proven strategies to ensure that and minimize the risk of system crash are as follows:

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Where are the Virtual Hard Disk Files Stored?

If it is a standalone host, by default, the Virtual Hard Disk files are stored in two different locations in Drive C: for the configuration files and the hard disk files.

Typically, the two locations where you will find the new VHD files are as follows:

Can a Virtual Hard Disk File be Deleted?

If you do not need to use a Virtual Hard Disk file anymore, you can delete it to free up some storage space in your computer system. You can do it from two different options namely, via Command Prompt or via Disk Management Console.

Detaching a VHD

When you are done working with the VHD, you may want to unmount the mounted virtual image. The simple steps to follow for it are:

You may note at this point that detaching the VHD will not delete it completely. It will simply remove it from the Disk Management window, and you will not see it when you open File Explorer, thereby making it unavailable for use.

To delete it completely using Command Prompt, the following steps are to be followed:

While using the Disk Management Console, follow these steps:

(You can alternatively press the Windows key and R key simultaneously to open the Run box and then type diskmgmt.msc and hit Enter)

This will delete the VHD file from the Disk Management system completely.

Virtual Hard Disk Vs Physical Hard Disk

What is the Size Limit for Virtual Hard Disks?

Ideally, there can be fixed and variable sizes, but the Virtual Hard Disk format, which is supported with all Hyper-V versions, comes with a maximum size limit of 2 terabytes (TB), or 2040 GB to be more precise.

Conclusion

Ideally, the Virtual Hard Disks format is very much similar to the hard drive but it is basically in a disk image file format with a .vhd file extension.

This means that it is very much portable and can be used in both a Virtual Machine as well as a physical machine.

There are different types of VHDs and are quite easy to use.