Sharing VM Images Across Virtualization Platforms

This document introduces several considerations related to sharing VM images across multiple virtualization platforms. Depending on the use case supported by your VM images, you may or may not care about your images' ability to address users of different virtualization platforms. Certainly in the case of desktop-based evaluation and desktop developer use cases, you want your images to be readily usable in all or most of the popular desktop virtualization platforms such as Sun xVM VirtualBox, VMware Workstation and Player, and Parallels.

In support of deployment use cases, it may be feasible for you to use VM image generation tooling such as rPath's rBuilder Online or your own customer build scripts to use a common bill of materials or recipes and generate images in different formats depending on the target virtualization platforms.

Popular Formats in Use Today

• VMDK - Virtual Machine Disk Format used in VMware platforms and supported, to some extent, on other platforms such as VirtualBox
• VDI - Virtual Disk Image format used in VirtualBox
• AMI - Amazon Machine Image

OVF - Open Virtual Machine Format

The Open Virtual Machine Format (OVF) is an emerging standard that goes beyond the VMDK format by enabling developers to specify relationships between multiple VM images. Although early support for OVF is available in several virtualization platforms, the format is not yet widely enough supported to be used as a viable format for sharing images across platforms.

Virtualization Platform-specific Additions

The host OS-based VirtualBox and VMware platforms offer software called "VirtualBox Guest Additions" and "VMware Tools" respectively, that can be installed in guest OS images to improve desktop performance and integration with the host OS. If you are delivering desktop-based images, you should consider pre-installing these additions in your VM images so as to reduce the number of steps required by your users.

Is VMDK Sufficient for VirtualBox, VMware and Other Popular Platforms?

Yes and no. For example, in VirtualBox 1.6, although VMDK format is generally supported, they are only supported as "write-through" images and snapshots are not supported. If users of your VM images don't need snapshot support, then you could deliver only in VMDK format and target both VirtualBox and VMware platforms. Otherwise, it would be helpful for you to set up your VM image build environment such that you can generate images in both VMDK and VDI formats.

There is also a number of conversion tools that help converting VM Image formats. The following article gives detailed insight to the compatibility of VirtualBox with the VMDK format and conversion of VMDK to VDI: How to convert from VMDK to VirtualBox

VMware ESX 3

VMware ESK Server uses a virtual disk file format different from the format used by VMware products that depend on a host OS. Refer to VMware's Virtual Machine Mobility Planning Guide for more information.

Amazon Machine Image (AMI)

If you target the Amazon EC2 platform, you will need to generate images in the AMI format.

VM Image format conversion

There is a number of conversion tools that help converting physical machine images to VM images (P2V converters) and various VM Image formats.