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Reporter RHNID:
Section: installing-preparing-ge-practice - Guided Exercise: Preparing for Installation
Language: en-US (English)
Workaround:

Description: In the student guide (chapter 2), we make the following statement:

Additionally, the overlay2 graph driver is used to store container images on each host. Docker supports a number of different graph driver configurations. See the documentation for the advantages and disadvantages of particular graph drivers.

However, Michael Phillips noted:

For some reason I though docker could use overlay/overlay2 or a logical volume, but not both. Maybe I'm wrong. Here is some text from Chapter 2 of the OCP 3.9 Installation & Configuration Guide. Maybe I'm just reading it incorrectly though:

For RHEL

The default storage back end for Docker on RHEL 7 is a thin pool on loopback devices, which is not supported for production use and only appropriate for proof of concept environments. For production environments, you must create a thin pool logical volume and re-configure Docker to use that volume.

Docker stores images and containers in a graph driver, which is a pluggable storage technology, such as DeviceMapper, OverlayFS, and Btrfs. Each has advantages and disadvantages. For example, OverlayFS is faster than DeviceMapper at starting and stopping containers, but is not Portable Operating System Interface for Unix (POSIX) compliant because of the architectural limitations of a union file system and is not supported prior to Red Hat Enterprise Linux 7.2. See the Red Hat Enterprise Linux release notes for information on using OverlayFS with your version of RHEL.

For more information on the benefits and limitations of DeviceMapper and OverlayFS, see Choosing a Graph Driver.

2.3.6.1. Configuring OverlayFS

OverlayFS is a type of union file system. It allows you to overlay one file system on top of another. Changes are recorded in the upper file system, while the lower file system remains unmodified.

Comparing the Overlay vs. Overlay2 Graph Drivers has more information about the overlay and overlay2 drivers.

For information on enabling the OverlayFS storage driver for the Docker service, see the Red Hat Enterprise Linux Atomic Host documentation.

2.3.6.2. Configuring Thin Pool Storage

You can use the docker-storage-setup script included with Docker to create a thin pool device and configure Docker's storage driver. This can be done after installing Docker and should be done before creating images or containers. The script reads configuration options from the /etc/sysconfig/docker-storage-setup file and supports three options for creating the logical volume:

Option A) Use an additional block device.

Option B) Use an existing, specified volume group.

Option C) Use the remaining free space from the volume group where your root file system is located.

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