8.  Configure autoextension of thin pools via an `lvm` profile.

    ```console
    $ sudo vi /etc/lvm/profile/docker-thinpool.profile
    ```

9.  Specify `thin_pool_autoextend_threshold` and `thin_pool_autoextend_percent`
    values.

    `thin_pool_autoextend_threshold` is the percentage of space used before `lvm`
    attempts to autoextend the available space (100 = disabled, not recommended).

    `thin_pool_autoextend_percent` is the amount of space to add to the device
    when automatically extending (0 = disabled).

    The example below adds 20% more capacity when the disk usage reaches
    80%.

    ```none
    activation {
      thin_pool_autoextend_threshold=80
      thin_pool_autoextend_percent=20
    }
    ```

    Save the file.

10. Apply the LVM profile, using the `lvchange` command.

    ```console
    $ sudo lvchange --metadataprofile docker-thinpool docker/thinpool

    Logical volume docker/thinpool changed.
    ```

11. Ensure monitoring of the logical volume is enabled.

    ```console
    $ sudo lvs -o+seg_monitor

    LV       VG     Attr       LSize  Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Monitor
    thinpool docker twi-a-t--- 95.00g             0.00   0.01                             not monitored
    ```

    If the output in the `Monitor` column reports, as above, that the volume is
    `not monitored`, then monitoring needs to be explicitly enabled. Without
    this step, automatic extension of the logical volume will not occur,
    regardless of any settings in the applied profile.

    ```console
    $ sudo lvchange --monitor y docker/thinpool
    ```

    Double check that monitoring is now enabled by running the
    `sudo lvs -o+seg_monitor` command a second time. The `Monitor` column
    should now report the logical volume is being `monitored`.

12. If you have ever run Docker on this host before, or if `/var/lib/docker/`
    exists, move it out of the way so that Docker can use the new LVM pool to
    store the contents of image and containers.

    ```console
    $ sudo su -
    # mkdir /var/lib/docker.bk
    # mv /var/lib/docker/* /var/lib/docker.bk
    # exit
    ```

    If any of the following steps fail and you need to restore, you can remove
    `/var/lib/docker` and replace it with `/var/lib/docker.bk`.

13. Edit `/etc/docker/daemon.json` and configure the options needed for the
    `devicemapper` storage driver. If the file was previously empty, it should
    now contain the following contents:

    ```json
    {
        "storage-driver": "devicemapper",
        "storage-opts": [
        "dm.thinpooldev=/dev/mapper/docker-thinpool",
        "dm.use_deferred_removal=true",
        "dm.use_deferred_deletion=true"
        ]
    }
    ```

14. Start Docker.

    **systemd**:

    ```console
    $ sudo systemctl start docker
    ```

    **service**:

    ```console
    $ sudo service docker start
    ```

15. Verify that Docker is using the new configuration using `docker info`.

    ```console
    $ docker info

    Containers: 0
     Running: 0
     Paused: 0
     Stopped: 0
    Images: 0
    Server Version: 17.03.1-ce
    Storage Driver: devicemapper
     Pool Name: docker-thinpool
     Pool Blocksize: 524.3 kB
     Base Device Size: 10.74 GB
     Backing Filesystem: xfs
     Data file:
     Metadata file:
     Data Space Used: 19.92 MB
     Data Space Total: 102 GB
     Data Space Available: 102 GB
     Metadata Space Used: 147.5 kB
     Metadata Space Total: 1.07 GB
     Metadata Space Available: 1.069 GB
     Thin Pool Minimum Free Space: 10.2 GB
     Udev Sync Supported: true
     Deferred Removal Enabled: true
     Deferred Deletion Enabled: true
     Deferred Deleted Device Count: 0
     Library Version: 1.02.135-RHEL7 (2016-11-16)
    <...>
    ```

    If Docker is configured correctly, the `Data file` and `Metadata file` is
    blank, and the pool name is `docker-thinpool`.

16. After you have verified that the configuration is correct, you can remove the
    `/var/lib/docker.bk` directory which contains the previous configuration.