Configuration of instance creation
----------------------------------
+Note: the minimum disk size accepted is 256MB, as ``debootstrap``
+requires disk space both for downloading the packages and installing
+them.
+
The kind of instance created can be customized via a settings file. This
file is not installed by default, as the instance creation will work
without it. The creation scripts will look for it in
model of using this OS but currently the OS interface in ganeti is
limiting.
+Creating OS variants
+--------------------
+
+Every Ganeti OS supports variants, so it's possible to define custom OS
+variants with instance-debootstrap as well. First, an additional variant has
+to be defined in ``$osdir/debootstrap/variants.list`` (with ``$osdir`` being
+``/usr/share/ganeti/os`` by default). Secondly, you can configure this
+instance variant in
+``$sysconfdir/ganeti/instance-debootstrap/variants/$variant.conf``, overriding
+the settings mentioned in the previous section.
+
+To use the newly created instance variant, specify it in ``gnt-instance`` like
+this::
+
+ gnt-instance add -o debootstrap+precise ...
+
+Example
++++++++
+
+To create a Ubuntu 12.04 (precise) instance variant, add the following to
+``$osdir/debootstrap/variants.list``::
+
+ precise
+
+Now create the file
+``$sysconfdir/ganeti/instance-debootstrap/variants/precise.conf`` with the
+following content::
+
+ MIRROR="http://archive.ubuntu.com/ubuntu/"
+ SUITE="precise"
+ COMPONENTS="main,universe"
+ ARCH="amd64"
+
+You can create Ubuntu 12.04 instances as follows::
+
+ gnt-instance add -t plain -o debootstrap+precise --disk 0:size=10000m -n node1.example.com instance1.example.com
+
+For this to work, make sure that you have the appropriate debootstrap script
+for precise (or just create a symlink called ``precise`` to ``gutsy`` in
+``/usr/share/debootstrap/scripts``).
+
+Instance creation parameters
+----------------------------
+
+Some aspects of the created instance can be conrolled via parameters at
+instance creation time with the ``-O`` parameter of ``gnt-instance``.
+
+The supported parameters are:
+
+- filesystem: the filesystem type to use for the root partition. This has to
+ be a filesystem type supported by ``mke2fs``. The default is 'ext4'.
+
Customization of the instance
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~