Image Format

Version 13 (Nikos Skalkotos, 11/24/2011 03:43 pm)

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h1. Image Format
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The image format (@img_format@) is a required OS Provider parameter and snf-image will complain if not found
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Right now we support 4 different types of image formats:
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* @extdump@
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* @ntfsdump@
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* @diskdump@
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* @custom@ _(unstable)_
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h2. extdump & ntfsdump image formats
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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.
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Partitions hosting a Windows or Linux system that are suitable for dumping should have the following properties:
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* Be the first partition in the filesystem
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* The OS they host should not depend on any other partitions
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* Start at sector 2048
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* Have a bootloader installed in the boot sector of the partition (not MBR)
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* Have the root device in /etc/fstab specified in a persistent way, using UUID or LABEL (for extdump only)
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h3. Known Issues
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* For linux systems, having grub installed in the partition is fragile and things can go wrong when resizing the partitions, especially when shrinking.
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* Swap space is not supported.
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* More complicated partition schemes are not supported.
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h2. diskdump image format
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Diskdump is a newer format that overcomes most of the aforementioned issues. This format is a raw copy (dd) of a whole disk.
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This design decision has the following benefits:
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* Swap partitions are supported
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* The system may use multiple partitions:
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** dedicated partitions for /boot, /home etc in linux
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** system and boot partition in Windows
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* There are no restrictions on starting sectors of partitions
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Although diskdump is a lot more flexible than the older formats, there are still some rules to follow:
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* All devices in fstab should be specified by persistent names (UUID or LABEL)
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* LVMs and extended partitions should be avoided.
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** The support for extended partitions is partial. snf-image does not support resizing logical partitions.
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** Logical volumes are not supported at all
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* In Linux disks only ext{2,3,4} filesystems are supported
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h2. Custom image Format
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For now, custom image format is a diskdump image format whose backend_id is a URL which defines the image to use.
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h2. Image Properties
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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.
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A list of mandatory and optional properties follows:
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* Mandatory properties (for @diskdump@ only)
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** *OSFAMILY={linux,windows}*
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This specifies whether the image is a Linux or a Windows Image. {ext,ntfs}dump formats are self descriptive regarding this property.
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** *ROOT_PARTITION={1,2,3,4}*
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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).
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* Optional properties
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** *USERS="username1 username2...."*
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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. 
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The rules we currently use are listed below:
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*** For Windows images, the @Administrator@'s password is reset.
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*** 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@.
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-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.-