Creating Partitions on Nodes

Creating Partitions on Nodes

Fuel generates Anaconda Kickstart scripts for Red Hat based systems and preseed files for Ubuntu to partition block devices on new nodes. Most of the work is done in the Cobbler script using the data from the “ks_spaces” variable generated by the Nailgun VolumeManager class based on the volumes metadata defined in the openstack.yaml release fixture.

Volumes are created following best practices for OpenStack and other components. Following volume types are supported:

an LVM volume group that can contain one or more volumes with type set to “lv”
plain non-LVM partition
a Linux software RAID-1 array of LVM volumes

Typical slave node will always have an “os” volume group and one or more volumes of other types, depending on the roles assigned to that node and the role-to-volumes mapping defined in the “volumes_roles_mapping” section of openstack.yaml.

There are a few different ways to add another volume to a slave node:

  1. Add a new logical volume definition to one of the existing LVM volume groups.
  2. Create a new volume group containing your new logical volumes.
  3. Create a new plain partition.

Adding an LV to an Existing Volume Group

If you need to add a new volume to an existing volume group, for example “os”, your volume definition in openstack.yaml might look like this:

- id: "os"
  type: "vg"
  min_size: {generator: "calc_min_os_size"}
  label: "Base System"
    - mount: "/"
      type: "lv"
      name: "root"
      size: {generator: "calc_total_root_vg"}
      file_system: "ext4"
    - mount: "swap"
      type: "lv"
      name: "swap"
      size: {generator: "calc_swap_size"}
      file_system: "swap"
    - mount: "/mnt/some/path"
      type: "lv"
        generator: "calc_LOGICAL_VOLUME_size"
        generator_args: ["arg1", "arg2"]
      file_system: "ext4"

Make sure that your logical volume name (“LOGICAL_VOLUME_NAME” in the example above) is not the same as the volume group name (“os”), and refer to current version of openstack.yaml for up-to-date format.

Adding Generators to Nailgun VolumeManager

The “size” field in a volume definition can be defined either directly as an integer number in megabytes, or indirectly via a so called generator. Generator is a Python lambda that can be called to calculate logical volume size dynamically. In the json example above size is defined as a dictionary with two keys: “generator” is the name of the generator lambda and “generator_args” is the list of arguments that will be passed to the generator lambda.

There is the method in the VolumeManager class where generators are defined. New volume generator ‘NEW_GENERATOR_TO_CALCULATE_SIZ’ needs to be added in the generators dictionary inside this method.

class VolumeManager(object):
    def call_generator(self, generator, *args):
        generators = {
            'NEW_GENERATOR_TO_CALCULATE_SIZE': lambda: 1000,

Creating a New Volume Group

Another way to add new volume to slave nodes is to create new volume group and to define one or more logical volume inside the volume group definition:

  type: "vg"
  min_size: {generator: "calc_NEW_VOLUME_NAME_size"}
  label: "Label for NEW VOLUME GROUP as it will be shown on UI"
    - mount: "/path/to/mount/point"
      type: "lv"
        generator: "another_generator_to_calc_LOGICAL_VOLUME_size"
        generator_args: ["arg"]
      file_system: "xfs"

Creating a New Plain Partition

Some node roles may be incompatible with LVM and would require plain partitions. If that’s the case, you may have to define a standalone volume with type “partition” instead of “vg”:

  type: "partition"
  min_size: {generator: "calc_NEW_PARTITION_NAME_size"}
  label: "Label for NEW PARTITION as it will be shown on UI"
  mount: "none"
  disk_label: "LABEL"
  file_system: "xfs"

Note how you can set mount point to “none” and define a disk label to identify the partition instead. Its only possible to set a disk label on a formatted portition, so you have to set “file_system” parameter to use disk labels.

Updating the Node Role to Volumes Mapping

Unlike a new logical volume added to a pre-existing logical volume group, a new logical volume group or partition will not be allocated on the node unless it is included in the role-to-volumes mapping corresponding to one of the node’s roles, like this:

    - {allocate_size: "min", id: "os"}
    - {allocate_size: "all", id: "image"}
  • controller - is a role for which partitioning information is given
  • id - is id of volume group or plain partition
  • allocate_size - can be “min” or “all” * min - allocate volume with minimal size * all - allocate all free space for volume, if several volumes have this key then free space will be allocated equally

Setting Volume Parameters from Nailgun Settings

In addition to VolumeManager generators, it is also possible to define sizes or whatever you want in the nailgun configuration file (/etc/nailgun/settings.yaml). All fixture files are templated using Jinja2 templating engine just before being loaded into nailgun database. For example, we can define mount point for a new volume as follows:

"mount": "{{settings.NEW_LOGICAL_VOLUME_MOUNT_POINT}}"

Of course, NEW_LOGICAL_VOLUME_MOUNT_POINT must be defined in the settings file.

Creative Commons Attribution 3.0 License

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.