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An Open Virtual Appliance (OVA) package is a single archive file, in the Tape Archive (.tar) format, containing
the files that comprise an OVF Package.

11.1.1.1. Selecting OVF or OVA Format

OVF packages contain a series of uncompressed files, which makes it easier if you want to access individual disk
images in the file. An OVA package contains one large file, and while you can compress this file, it does not give
you the flexibility of a series of files.
Using the OVA format is useful for specific applications for which it is beneficial to have just one file, such as
creating packages for Web downloads. Consider using OVA only as an option to make the package easier to
handle. Using this format lengthens both the export and import processes.
11.1.2. Disk Image Formats (VHD and VMDK)
Using XenCenter, you can import disk images in the Virtual Hard Disk (VHD) and Virtual Machine Disk (VMDK)
formats. Exporting standalone disk images is not supported.
Note:
To import disk images, you must be logged in as root or have the Pool Administrator Role
Based Access Control (RBAC) role associated with your user account.
You might choose to import a disk image when a virtual disk image is available without any associated OVF
metadata. Situations in which this might occur include:
• It is possible to import a disk image, but the associated OVF metadata is not readable
• A virtual disk is not defined in an OVF package
• You are moving from a platform that does not allow you to create an OVF package (for example, older platforms
or images)
• You want to import an older VMware appliance that does not have any OVF information
• You want to import a standalone VM that does not have any OVF information
When available, Citrix recommends importing appliance packages that contain OVF metadata rather than an
individual disk image. The OVF data provides information the Import wizard requires to recreate a VM from its disk
image, including the number of disk images associated with the VM, the processor, storage, network, memory
requirements and so on. Without this information, it can be much more complex and error-prone to recreate
the VM.
11.1.3. XVA Format
XVA is a virtual appliance format specific to XenServer, which packages a single VM as a single set of files, including
a descriptor and disk images. The filename extension is .xva.
The descriptor (file extension ova.xml) specifies the virtual hardware of a single VM.
The disk image format is a directory of files. The directory name corresponds to a reference name in the descriptor
and contains 2 files for each 1 MB block of the disk image. The base name of each file is the block number in
decimal. The first file contains 1 block of the disk image in raw binary format and does not have an extension.
The second file is a checksum of the first file, with the extension .checksum.
Important:
If a VM is exported from a XenServer host and then imported into another XenServer host
with a different CPU type, it may not run properly. For example, a Windows VM created
on a XenServer host with an Intel® VT Enabled CPU, and then exported, may not run when
imported into a XenServer host with an AMD-VTM CPU.