Volume allocation¶

Fuel defines a set of rules for existing roles. The rules determine disk space usage on the nodes with the specified role. Fuel partitions the disk drives assigned to the node in accordance with these rules.

Using the Fuel web UI, you can also tweak the disk size for a predetermined partition on the node before the deployment.

The plugin framework allows you to change the predefined rules and to specify new rules for the plugin-specific roles using the file volumes.yaml in the plugin root directory.

The syntax of the volumes.yaml file follows the same conventions used to define volumes for the standard Fuel roles. For reference, see Creating Partitions on Nodes and an example of partitioning rules.

There are two primary use cases with volumes.yaml:

• Defining the disk allocation for a new role.
• Redefining the disk allocation for the existing role.

Define disk allocation for a new role

An example of an automatically generated volumes.yaml:

volumes_roles_mapping:
 # Default role mapping
 fuel-plugin-example_role:
  - {allocate_size: "all", id: "os"}

# Set here new volumes for your role
volumes: []

The two sections are:

• volumes_roles_mapping – defines which volumes the nodes with the given role will contain; the volumes are Fuel-defined and plugin-specific. In the given example, there is only one rule: all the disk size is assigned to one volume named "os". This is also the default rule, which means that even if you define a new role but do not provide volume mapping for it, it will be used implicitly.
• volumes – contains the definition of plugin-specific volumes. In the given example, there are no plugin-specific volumes defined.

To assign a minimal size to the OS VG and create a raw partition on all of the remaining space:

1. Edit volumes.yaml:

   volumes_roles_mapping:
    fuel-plugin-example_role:
     - {allocate_size: "min", id: "os"}
     - {allocate_size: "all", id: "fuel-plugin-example-raw_partition"}
   
   volumes:
    - id: fuel-plugin-example-raw_partition
      type: partition
      min_size:
       generator: calc_gb_to_mb
       generator_args: [10]
      label: "Example Plugin raw partition"
      mount: none
      disk_label: "example"
      file_system: none
   

2. Synchronize the edited volumes.yaml using fuel plugins --sync.

3. In the Fuel web UI, add a new node with the plugin’s role.

Redefine disk allocation for an existing role

An example of adding two plugin-specific volume groups to the standard controller role:

volumes_roles_mapping:
 compute:
  - {allocate_size: "min", id: "os"}
  - {allocate_size: "all", id: "vm"}
  - {allocate_size: "min", id: "example1"}
  - {allocate_size: "min", id: "example2"}

# Set here new volumes for your role
volumes:
  - id: "example1"
    type: "vg"
    min_size:
     generator: "calc_gb_to_mb"
     generator_args: [5]
    label: "Example 1"
    volumes:
     - mount: "/example1"
       type: "lv"
       name: "example1"
       size:
        generator: "calc_total_vg"
        generator_args: ["example1"]
       file_system: "ext4"
  - id: "example2"
    type: "vg"
    min_size:
     generator: "calc_gb_to_mb"
     generator_args: [10]
    label: "Example 2"
    volumes:
     - mount: "/example2"
       type: "lv"
       name: "example2"
       size:
        generator: "calc_total_vg"
        generator_args: ["example2"]
       file_system: "xfs"

Although allocation of volumes for existing roles can be redefined by a plugin, existing volumes definition cannot be changed; there will be no error message, but you will not be able to open the settings for the environment. If you need to redefine the partitioning for the already existing roles, the only way to do that is to define your own volumes and replace the standard one with them in the mappings. We do not recommend this approach, though, as it makes the plugin incompatible with other plugins, as well as with any updates.