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Users have different formats available to store virtual machine disk files. On VMware products, the VMware-specific Virtual Machine Disk file is used as a default.
This file format isn't compatible with other virtualization offerings, though, which is why VMware Workstation offers an option to export files to open virtualization format (OVF). In this article, you'll learn under which circumstances this may be useful.
There are about as many Virtual Machine Disk (VMDK) files as there are virtualization products. Microsoft uses the vhd or vhdx file, Oracle Virtualbox uses OVF file as the default, and open source offerings use raw files as well as qcow2 files. Several features are provided by each of these different offerings. An important feature is support for thin provisioning, as well as the ability to manage snapshot support by a VMDK file. Alternatively, it's possible to just keep it simple and have the virtualization software use raw device access, also referred to as pass-through.
With so many choices, there is, unfortunately, a lack of standardization. A virtual disk file that was created in one virtualization product cannot easily by read by an alternative virtualization product. This problem can be mitigated by the OVF file format, a standard that was developed to make it easy to build virtual appliances that can be included in alternative virtualization platforms. The OVF file standard was submitted in 2007 by all of the major players in virtualization at that time: VMware, Microsoft, XenSource, Dell Technologies (formerly, Dell), Hewlett Packard Enterprise (formerly, HP), and IBM.
OVF goes beyond delivering a mere disk file, though. OVF includes a file containing metadata in addition to the disk image file, comparable to what is stored in the VMX file of the VM in a typical VMware environment. This metadata file contains information such as the name, hardware requirements and, potentially, references to other files that are contained in the OVF package.
VMware Workstation OVF support
Even though OVF file was adopted by VMware as early as 2007, VMware is still using VMDK and VMX as the standard file formats. VMware has supported OVF file since VMware Workstation 6.5. This support means that VMware Workstation can read OVF files, but not before the files have been converted to the standard VMware VMDK file format. This conversion can take a significant amount of time, as the entire disk file needs to be processed.
You'll also be able to export OVF files from VMware Workstation, but what is true for an import goes for the export as well: VMDK remains the default file format in VMware Workstation.
The primary motivation behind VMware's support for the OVF file format seems to be an increased compatibility. After exporting a disk file to OVF, it will be possible -- through other virtualization offerings -- to read the disk file as well. However, this support comes with some drawbacks: While exporting a VMware Workstation file to OVF, there's still some remaining disk metadata that makes it impossible to import the disk file seamlessly.
Due to the limited support for OVF files throughout the different virtualization offerings, it is reasonable to ask just how useful OVF really is. While this utility is certainly useful, its limitations indicate that we're still some time away from the day when each virtualization product can convert VMDK files without additional work.
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