Image Format

Version 9 (Constantinos Venetsanopoulos, 11/24/2011 11:34 am) → Version 10/39 (Nikos Skalkotos, 11/24/2011 02:40 pm)

h1. Image Format

The image format (@img_format@) is a required OS Provider parameter and snf-image will complain if not found
Right now we support 3 different types of image formats:
* @extdump@
* @ntfsdump@
* @diskdump@

h2. extdump & ntfsdump

Those two formats are raw copies (using dd) of partitions hosting Linux systems on ext{2,3,4} and Windows systems on ntfs filesystems respectively.

Partitions hosting a Windows or Linux system that are suitable for dumping should have the following properties:
* Be the first partition in the filesystem
* The OS they host should not depend on any other partitions
* Start at sector 2048
* Have a bootloader installed in the partition
* Have the root device in /etc/fstab specified in a persistent way, using UUID or LABEL (for extdump only)

h3. Known Issues

* For linux systems, having grub installed in the partition is fragile and things can go wrong when resizing the partitions, especially when shrinking.
* Swap space is not supported.
* More complicated partition schemes are not supported.

h2. diskdump

Diskdump is a newer format that overcomes most of the aforementioned issues. This format is a raw copy (dd) of a whole disk.

This design decision has the following benefits:
* Swap partitions are supported
* The system may use multiple partitions:
** dedicated partitions for /boot, /home etc in linux
** system and boot partition in Windows
* There are no restrictions on starting sectors of partitions

Although diskdump is a lot more flexible than the older formats, there are still some rules to follow:
* All devices in fstab should be specified by persistent names (UUID or LABEL)
* LVMs and extended partitions should be avoided.
** The support for extended partitions is partial. snf-image does not support resizing logical partitions.
** Logical volumes are not supported at all
* In Linux disks only ext{2,3,4} filesystems are supported

h3. Image Properties

In order for snf-image to be able to properly configure an image, image of @diskdump@ format, it may make use of needs to be passed a set of image properties. Those image properties are passed to snf-image by Ganeti through the @img_poroperties@ OS parameter. For the @diskdump@ format some properties are *mandatory*. For older formats ({ext,ntfs}dump) all image properties are optional. properties:

A list of mandatory and optional properties follows:
* Mandatory properties (for @diskdump@ only)
This specifies whether the image is a Linux or a Windows Image. {ext,ntfs}dump formats are self descriptive regarding this property.

This specifies the partition number of the root partition. As mentioned earlier, for now we only support primary partitions. For {ext,ntfs}dump formats this property is trivial (they host only one partition).

* Optional properties
*USERS="username1 username2...."*
This is a list of users, whose password will be reset by snf-image.

All image properties are passed to snf-image through the @img_properties@ OS parameter. The @img_properties@ parameter is *mandatory* when trying to deploy an image of @diskdump@ format. @img_properties@ should be a json file dumped as a string. When trying to deploy an image of type @{ext,ntfs}dump@ then @img_properties@ are not necessary.