github.com/jlmeeker/kismatic@v1.10.1-0.20180612190640-57f9005a1f1a/ansible/roles/docker/tasks/direct_lvm.yaml

---
  - name: install lvm2 package
    package:
      name: lvm2
      state: present
  - name: create docker volume group
    lvg:
      pvs: "{{ docker.storage.direct_lvm_block_device.path }}"
      state: present
      vg: docker
  - name: create thinpool logical volume
    lvol:
      lv: thinpool
      vg: docker
      size: "{{ docker.storage.direct_lvm_block_device.thinpool_percent }}%VG" # Use 95% of the volume group for this logical volume
      opts: --wipesignatures y
  
  # The following two tasks are used to enable this play to be idempotent. We detect whether
  # the logical volume (LV) is already a thin LV using `lvs`, which returns a list
  # of all the LVs. `lvs` also displays the LV attributes in the
  # lvattr field. According to the `lvs` manpage, the first bit in the attribute list determines
  # the LV type. A value of "t" in this bit means "thin pool".
  # See `man lvs` for more details.
  # Sample output when the "thinpool" LV is of type thin pool:
  # > lvs -o lvname,lvattr --no-headings
  # thinpool     twi-aot---
  - name: list logical volumes
    command: lvs -o lvname,lvattr --noheadings
    register: logical_volume_list
  - name: determine if thin pool conversion is necessary
    set_fact:
      requires_thin_pool_conversion: True
    # Regex: match whitespace, the name of the thin pool, whitespace, and then any character other than 't' or ' '. 
    # If the item doesn't match, this means that the "thinpool" LV is already a thin pool, 
    # and no conversion is necessary.
    when: item | match("\s+thinpool\s+[^t ]+")
    with_items: "{{ logical_volume_list.stdout_lines }}"
    # ^ TODO: lvs command can output json. Use json when we bump ansible version to 2.2
    # when: item.lv_name == "thinpool" and item.lv_attr | match("^t")
    # with_items: "{{ logical_volume_list.stdout | json_query('report.lv') }}"
  
  
  # When a thin pool LV is created, two standard LVs are combined into a single thin pool LV.
  # The two standard volumes are a data volume and a metadata volume. The resulting combined thin pool takes the name of the 
  # data LV (in our case 'thinpool'), and the metadata volume is no longer "listed" as an LV.
  # For this reason, we only create the "thinpoolmeta" LV if the thin pool LV has not been created yet.
  # If we don't have this check, this would result in an extra LV called "thinpoolmeta" whenever this play 
  # is re-run.
  # More info can be found in `man lvmthin`
  - name: create thinpoolmeta logical volume
    lvol:
      lv: thinpoolmeta
      vg: docker
      size: "{{ docker.storage.direct_lvm_block_device.thinpool_metapercent }}%VG" # Use 1% of the volume group for this logical volume
      opts: --wipesignatures y
    when: requires_thin_pool_conversion is defined and requires_thin_pool_conversion|bool == true
  
  # This is where we create the thin pool LV, using the docker/thinpool LV
  # for storing the data, and the docker/thinpoolmeta LV for the thin pool's metadata
  - name: convert the pool to a thin pool
    command: lvconvert -y --zero n -c 512K --thinpool docker/thinpool --poolmetadata docker/thinpoolmeta
    when: requires_thin_pool_conversion is defined and requires_thin_pool_conversion|bool == true
  - name: create auto extension profile
    template:
      src: docker-thinpool.profile
      dest: /etc/lvm/profile/docker-thinpool.profile
  - name: apply lvm profile
    command: lvchange --metadataprofile docker-thinpool docker/thinpool
  - name: enable monitoring to ensure autoextend executes
    command: lvchange --metadataprofile docker-thinpool docker/thinpool