OVF: Folders of files / OVA: All-in-one
OVF is an open standard, specified by the Distributed Management Task Force (DMTF), for packaging and distributing a virtual appliance consisting of one or more virtual machines (VMs).
An OVF Package is composed of metadata and file elements that describe virtual machines, plus additional information that is important to the deployment and operation of the applications in the OVF package. Its file extension is .ovf
An Open Virtual Appliance (OVA) is an OVF Package in a single file archive with the .ova extension.
An OVA package is a single archive file, in the Tape Archive (tar) format, containing the files that comprise an OVF Package.
What's in an OVF package? An OVF Package always includes a descriptor file (*.ovf) and may also include a number of other files
| File type | Description |
| Descriptor | The descriptor is the main document of an OVF package that specifies the virtual hardware requirements of the service and can also include other information such as descriptions of virtual disks, the service itself, and guest operating systems, a license agreement (EULA), instructions to start and stop VMs in the appliance, and instructions to install the service. The descriptor file extension is .ovf |
| Manifest | The manifest is an SHA-1 digest of every file in the package (except for the .mf and .cert files themselves), allowing the package contents to be verified by detecting any corruption and used for integrity and authenticity checks. The manifest file extension is .mf |
| Signature | The signature is the digest of the manifest signed with the public key from the X.509 certificate included in the package, and allows the package author to be verified. they must be in the same directory as the OVF descriptor and have the same base name, The signature file extension is .cert |
| Virtual disks | OVF does not specify a disk image format. An OVF package includes files comprising virtual disks in the format defined by the virtualization product that exported the virtual disks. XenServer produces OVF packages with disk images in Dynamic VHD format; VMware products and Virtual Box produce OVF packages with virtual disks in Stream-Optimized VMDK format. |
Note: Optional resource files (such as ISO's) can be part if OVF package as well if the .iso image where attached to the VM and you can chose it when you taking a OVF template.
Metadata is data that describes other data. Meta is a prefix that in most information technology usages means 'an underlying definition or description.'
Metadata summarizes basic information about data, which can make finding and working with particular instances of data easier. For example, author, date created and date modified and file size are examples of very basic document metadata. Having the abilty to filter through that metadata makes it much easier for someone to locate a specific document.
In addition to document files, metadata is used for images, videos, spreadsheets and web pages. The use of metadata on web pages can be very important. Metadata for web pages contain descriptions of the page's contents, as well as keywords linked to the content. These are usually expressed in the form of metatags. The metadata containing the web page's description and summary is often displayed in search results by search engines, making its accuracy and details very important since it can determine whether a user decides to visit the site or not.
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