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Update documentation about partition clones

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Using the root_clone attribute comes with some requirements
and consequences. This commit documents them
This commit is contained in:
Marcus Schäfer 2024-02-14 15:42:39 +01:00
parent 765c5a5e28
commit 97aef9904b
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2 changed files with 26 additions and 4 deletions
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2
doc/source/conf.py
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@ -195,8 +195,6 @@ html_sidebars = {
html_theme = "sphinx_rtd_theme"
html_static_path = ['.static']
html_theme_options = {
'collapse_navigation': False,
'display_version': False

28
doc/source/working_with_images/clone_partitions.rst
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@ -33,6 +33,11 @@ Let's take a look at the following example:
<partitions>
<partition name="home" size="10" mountpoint="/home" filesystem="ext3" clone="2"/>
</partitions>
<oemconfig>
<oem-systemsize>2048</oem-systemsize>
<oem-resize>false</oem-resize>
</oemconfig>
<size unit="G">100</size>
</type>
With the above setup {kiwi} will create a disk image that
@ -48,8 +53,8 @@ contains the following partition table:
5 1275904 1296383 10.0 MiB 8300 p.lxhomeclone1
6 1296384 1316863 10.0 MiB 8300 p.lxhomeclone2
7 1316864 1337343 10.0 MiB 8300 p.lxhome
8 1337344 3864575 1.2 GiB 8300 p.lxrootclone1
9 3864576 6287326 1.2 GiB 8300 p.lxroot
8 1337344 3864575 2 GiB 8300 p.lxrootclone1
9 3864576 6287326 2 GiB 8300 p.lxroot
When booting the system only the origin partitions `p.lxboot`, `p.lxroot`
and `p.lxhome` will be mounted and visible in e.g. :file:`/etc/fstab`,
@ -67,6 +72,25 @@ can hold that many partitions).
There is a limit how many partitions a partition table can hold.
This also limits how many clones can be created.
It's important when using the `root_clone` attribute to specify a size for
the part of the system that represents the root partition. As of today {kiwi}
does not automatically divide the root partition into two identical pieces.
In order to create a clone of the partition a size specification is required.
In the above example the size for root is provided via the `oem-systemsize`
element. Using a root clone and fixed size values has the following consequences:
1. The resize capability must be disabled. This is done via `oem-resize`
element. The reason is that only the last partition in the partition
table can be resized without destroying data. If there is a clone of
the root partition it should never be resized because then the two
partitions will be different in size and no longer clones of each other
2. There can be unpartitioned space left. In the above example the overall
disk size is set to 100G. The sum of all partition sizes will be smaller
than this value and there is no resize available anymore. Depending
on the overall size setup for the disk this will leave unpartitioned
space free on the disk.
Use Case
--------