Wikipedia defines OVF as an Open… no I won’t go there 🙂
For the sake of topic though, I will briefly explain OVF vs OVA. Open Virtualization Format (OVF) is an open standard. It’s a way of packaging and distributing virtual appliances in a platform independent way. An OVF package will consist of a number of files. It will contain an OVF descriptor file in XML format, disk image file/s, and optionally certificate and auxiliary files.
OVA or OVA package on the other hand is simply a tar archive of an OVF package folder in a single file.
Creating an OVF in vCenter is really simple. The VM does need to be off to create the OVF.
Using the Web Client right click the VM and select All vCenter Actions. Select Export OVF Template.
The Export OVF Template window will open. The Name field will be pre-populated with the name of the VM. Select a directory location. Check the Overwrite existing files checkbox if you have an old export you want to overwrite. Then select a Format (OVF or OVA). If OVF is selected a directory will be create under the folder you selected. If OVA is selected a single file will be created in the directory you selected.
New in vCenter 5.1 is the Advanced option. It’s highly unlikely you need to select anything here. I’ve seen this referred to as a lossless OVF export. Apart from preserving the UUID and MAC, the extra configuration checkbox will preserve the PCI slot numbers and boot order.
Click OK and the OVF will be created. Whether you select OVF or OVA the virtual disks will be compressed during the export conserving storage.
There is also a command line utility called OVF Tool. The VMware Community link is below. OVF Tool is a good way of creating automation scripts. It contains a rich set of command line options to are not normally available via the vCenter client.