Preface

The Red Hat Enterprise Linux OpenStack Platform (RHEL OSP) Director provides two methods for using Ceph as a backend for Glance, Cinder, Cinder Backup and Nova:

  1. OpenStack Creates the Ceph Cluster: OpenStack Director can spin up a Ceph cluster, which requires configuring templates for the Ceph OSDs. OpenStack handles the installation and configuration of Ceph nodes. In this scenario, OpenStack will install Ceph monitors with OpenStack controller nodes.
  2. OpenStack Connects to an Existing Ceph Cluster: OpenStack Director (RHEL OSP9 and beyond) can connect to a Ceph monitor and configure the Ceph cluster for use as a backend for OpenStack.

The foregoing methods are the preferred methods for configuring Ceph as a backend for OpenStack, because they will handle much of the installation and configuration automatically. See Red Hat OpenStack Platform for additional details.

This document details the manual procedure for configuring Ceph, QEMU, libvirt and OpenStack to use Ceph as a backend. This document is intended for use for those who do not intend to use the RHEL OSP Director.

Diagram
NOTE
A running Ceph storage cluster and at least one OpenStack node is required to use Ceph Block Devices as a backend for OpenStack.

Three parts of OpenStack integrate with Ceph’s block devices:

  • Images: OpenStack Glance manages images for VMs. Images are immutable. OpenStack treats images as binary blobs and downloads them accordingly.
  • Volumes: Volumes are block devices. OpenStack uses volumes to boot VMs, or to attach volumes to running VMs. OpenStack manages volumes using Cinder services. Ceph can serve as a black end for OpenStack Cinder and Cinder Backup.
  • Guest Disks: Guest disks are guest operating system disks. By default, when booting a virtual machine, its disk appears as a file on the filesystem of the hypervisor (usually under /var/lib/nova/instances/<uuid>/`). OpenStack Glance can store images in a Ceph Block Device, and can use Cinder to boot a VM using a copy-on-write clone of an image.
Important

Ceph doesn’t support QCOW2 for hosting a virtual machine disk. To boot virtual machines in Ceph (ephemeral backend or boot from volume), the Glance image format must be RAW.

OpenStack can use Ceph for images, volumes or guest disks VMs. There is no requirement to use all three.