Image Format

Version 15 (Nikos Skalkotos, 11/24/2011 04:06 pm) → Version 16/39 (Nikos Skalkotos, 11/24/2011 04:10 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 4 different types of image formats:
* @extdump@
* @ntfsdump@
* @diskdump@
* @custom@ _(unstable)_

h2. extdump & ntfsdump image formats

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 boot sector of the partition (not MBR)
* 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 image format

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

h2. Custom image Format

For now, a custom image is a diskdump image whose @img_id@ OS Parameter (see [[:#Ganeti-OS-Interface|Ganeti OS Interface]]) is a URL that points to the image file.

h2. Image Properties

In order for snf-image to be able to properly configure an image, it may make use of 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.

A list of mandatory and optional properties follows:
* Mandatory properties (@diskdump@ (for @diskdump@ only)
** *OSFAMILY={linux,windows}*
This specifies whether the image is a Linux or a Windows Image. {ext,ntfs}dump formats are self descriptive regarding this property.
** *ROOT_PARTITION={1,2,3,4}*
This specifies the partition number of the root partition. As mentioned earlier, for now, only primary partitions are supported. This property is trivial for {ext,ntfs}dump formats (they only host one partition).
* Optional properties
** *USERS="username1 username2...."*
This is a space-seperated list of users, whose password will be reset by snf-image. If this is missing then those users are chosen according to a set of rules, but please do not depend on this. Those rules may change or even be dropped in the future. Do directly specify the @USERS@ list, just to be on the safe side.
The rules we currently use are listed below:
*** For Windows images, the @Administrator@'s password is reset.
*** For Linux images, the root password is reset for all distribution. If @snf-image@ detects the system as a Fedora or an Ubuntu Linux, then it also resets the password of the user with username @user@.

-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.-