You may have encountered files such as VDI, VHD, VMDK, and VHDX when saving, downloading, or setting up virtual machine environments. These files are known as virtual disk image files and are used to store virtual disk images and configurations required for running virtualized operating systems.
Now, as you might expect, each disk image format has its pros and cons, so when should you use either option, and for what purpose?
What Is VDI?
VDI (Virtual Disk Image) is an open-source virtual disk format developed for Oracle’s VirtualBox hypervisor. Its open-source nature allows VDI cross-platform support from other popular hypervisors such as VMware and Windows Hyper-V.
A .vdi file is created by saving a machine state through VirtualBox’s Virtual Media Manager. The file can be copied and shared for anyone to use. Loading the file into VirtualBox provides users with the option for fixed and dynamically allocated storage. Dynamically allocated storage allows users to keep expanding the file without worrying about file size, while fixed allocation can help control file size by allocating a set amount of memory for the virtual machine.
Supported by most hypervisors running on different operating systems
Slower than VMDK and VHDX
Option for dynamic and fixed memory allocation
Does not support incremental backups
Performs better than VHD and VHDX
Very portable
VDI is a great virtual disk image for anyone using VirtualBox. It is free, open-source, has great cross-platform support, and is portable. Running a VDI file through VirtualBox allows users to enjoy features, such as remote access, snapshotting, anddirect USB access on Windows, which are offered as premium on other hypervisors. Furthermore, withthe newest VirtualBox release, Linux users get secure boot support!
What Are VHD and VHDX?
VHD and VHDX are disk image formats developed by Microsoft. VHD stands for Virtual Hard Disk and is the format used in older Microsoft virtualization products such as Microsoft Virtual PC and Microsoft Virtual Server. Although development has ceased, VHD is still used in the newer Microsoft Hyper-V hypervisor for various legacy applications.
VHDX stands for Virtual Hard Disc v2. It is the successor of the older VHD format and primarily runs on Microsoft Hyper-V. VHDX provides several improvements over VHD, providing a maximum of 64TB of disk space, improved overall performance, better security and resilience, and third-party support for other platforms such as VirtualBox, VMware, and Citrix XenServer.
VHD and VHDX are primarily used onType 1 hypervisorslike Hyper-V, which provides better efficiency and performance but at the cost of possible host PC vulnerabilities.
Repair and recovery capabilities
Guest operating systems are more susceptible to various malware attacks
One virtual machine can have multiple users
Corrupted VHD and VHDX files can crash Windows
Each user doesn’t affect other instances of the virtual machine
Requires technical understanding to use advanced features
Feature-rich for advanced server virtualization
Limited support for non-Windows operating systems, especially VHDX
VHD is supported by numerous virtualization tools
VHDX is largely limited to Hyper-V
VHD and VHDX disc image formats are best used by system administrators already using Microsoft Hyper-V and other Microsoft-related products. Its headless operation feature makes administration much easier, but it will require knowledge of Windows PowerShell to use the CLI. If you’re new to virtualization, you’ll want to skip this format and use a more general-purpose disk image format like VDI and VMDK.
What Is VMDK?
The VMDK file format was first developed exclusively for VMWare’s virtualization products, such as the Workstation Pro and Workstation Player hypervisors. However, after some revisions in 2011, VMDK was made an open format for better interoperability across different platforms. VMDK files can now be run using VirtualBox, QEMU, Hyper-V, Workstation Pro, and Workstation Player.
VMWare’s virtualization products offer many advanced features that add functionalities and make handling VMs much more convenient. Running VMDK through VMWare’s Workstation hypervisors provides users with incremental backups, quick and convenient snapshots, the ability to revert to older saved machine states, live migration, and overall faster performance compared to VHD and VDI.
Cross-platform support
Doesn’t work on Microsoft Hyper-V
Better overall performance
Advanced features only available on Workstation Pro
Migration from one host to another without disrupting regular operation
Incremental backups
VMDK is best used by people who already bought or are willing to buy Workstation Pro. You get a ton of features, such as encrypted VMs, snapshots, remote connection, and containers, plus great performance when compared to other hypervisors. For example, the free Workstation Players still perform better than VirtualBox. However, you will miss out on extra features. So, if you cannot justify buying a Workstation Pro license, use Workstation Player for faster processing and VirtualBox with VMDK for features like snapshotting and remote access.
What About ISO?
Optical Disc Image (ISO) is not a virtual disk format but rather a file format used for optical disc images. It is commonly used for storing a copy of a CD or DVD’s content, which can be used for installation or running software. ISO files are not specifically designed for virtualization. However, since they are used in cloning memory drives, hypervisors can still mount them virtually, access their files, and function like a regular VM.
ISO files are great for distributing OS images on the internet. However, using them for virtualization requires a more detailed setup and potentially misses out on performance and features. So, make sure you download virtual disk images instead of ISO files when available. Using these specialized formats saves you time during configuration and will already have compatible features the first time you boot your machine.
Can You Convert Virtual Disk Image Formats?
It is possible to convert virtual disk image files to other formats. Although VDI, VHD, VHDX, and VMDK can run on most popular hypervisors, many still convert their virtual image files to other formats to ensure feature compatibility when migrating to other platforms.
One of the simplest ways to convert virtual image files to other formats is through the tools already provided within VirtualBox and VMware Workstation. The VirtualBox Virtual Media Manager can convert ISO, VHD, VHDX, and VMDK to VDI. Similarly, the virtual machine wizard in VMware Workstation can be used to open ISO, VDI, VHD, and VHDX to save them as VMDK.
For those looking to convert VDH and VHDX to other formats and vice versa, you will have to download the Microsoft Virtual Machine Converter. More advanced users may convert multiple virtual disc images through PowerShell and VBoxCommands.
Don’t Lose Out on Performance and Features
Virtual disk image formats have been developed to ensure feature compatibility of disk images and hypervisors. Although VDI, VHD, VHDX, and VMDK have cross-platform support, having them run on hypervisors not specifically made for them will mean missing out on valuable performance and features. Ideally, you should use VDI for VirtualBox, VHD and VHDX on Hyper-V, and VMDK for Workstation. For one-off situations, you can use them with whatever hypervisor you have. But for longer use cases, you will want to consider converting your images instead.
