Chapter 1. Introduction

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Red Hat OpenStack Platform director creates a cloud environment called the overcloud. You can use director to configure extra features for an overcloud, including integration with Red Hat Ceph Storage (both Ceph Storage clusters created with the director or existing Ceph Storage clusters).

This guide includes instructions about how to integrate an existing Ceph Storage cluster with an overcloud. This means that director configures the overcloud to use the Ceph Storage cluster for storage needs. You manage and scale the cluster itself outside of the overcloud configuration.

This guide contains instructions for deploying a containerized Red Hat Ceph Storage cluster with your overcloud. Director uses Ansible playbooks provided through the ceph-ansible package to deploy a containerized Ceph cluster. The director also manages the configuration and scaling operations of the cluster.

For more information about containerized services in Red Hat OpenStack Platform (RHOSP), see Configuring a basic overcloud with the CLI tools in the Director Installation and Usage guide.

1.1. Introduction to Ceph Storage

Red Hat Ceph Storage is a distributed data object store designed to provide excellent performance, reliability, and scalability. Distributed object stores are the future of storage, because they accommodate unstructured data, and because clients can use modern object interfaces and legacy interfaces simultaneously. At the core of every Ceph deployment is the Ceph Storage cluster, which consists of several types of daemons, but primarily, these two:

Ceph OSD (Object Storage Daemon)
Ceph OSDs store data on behalf of Ceph clients. Additionally, Ceph OSDs utilize the CPU and memory of Ceph nodes to perform data replication, rebalancing, recovery, monitoring and reporting functions.
Ceph Monitor
A Ceph monitor maintains a master copy of the Ceph storage cluster map with the current state of the storage cluster.

For more information about Red Hat Ceph Storage, see the Red Hat Ceph Storage Architecture Guide.

1.2. Requirements

This guide contains information supplementary to the Director Installation and Usage guide.

Before you deploy a containerized Ceph Storage cluster with your overcloud, your environment must contain the following configuration:


The Ceph Monitor service installs on the overcloud Controller nodes, so you must provide adequate resources to avoid performance issues. Ensure that the Controller nodes in your environment use at least 16 GB of RAM for memory and solid-state drive (SSD) storage for the Ceph monitor data. For a medium to large Ceph installation, provide at least 500 GB of Ceph monitor data. This space is necessary to avoid levelDB growth if the cluster becomes unstable. The following examples are common sizes for Ceph storage clusters:

  • Small: 250 terabytes
  • Medium: 1 petabyte
  • Large: 2 petabytes or more.

If you use the Red Hat OpenStack Platform director to create Ceph Storage nodes, note the following requirements.

1.2.1. Ceph Storage node requirements

Ceph Storage nodes are responsible for providing object storage in a Red Hat OpenStack Platform environment.

For information about how to select a processor, memory, network interface cards (NICs), and disk layout for Ceph Storage nodes, see Hardware selection recommendations for Red Hat Ceph Storage in the Red Hat Ceph Storage Hardware Guide. Each Ceph Storage node also requires a supported power management interface, such as Intelligent Platform Management Interface (IPMI) functionality on the motherboard of the server.


Red Hat OpenStack Platform (RHOSP) director uses ceph-ansible, which does not support installing the OSD on the root disk of Ceph Storage nodes. This means that you need at least two disks for a supported Ceph Storage node.

Ceph Storage nodes and RHEL compatibility

  • RHOSP 16.1 is supported on RHEL 8.2. However, hosts that are mapped to the Ceph Storage role update to the latest major RHEL release. Before upgrading to RHOSP 16.1 and later, review the Red Hat Knowledgebase article Red Hat Ceph Storage: Supported configurations.

Placement Groups (PGs)

  • Ceph Storage uses placement groups (PGs) to facilitate dynamic and efficient object tracking at scale. In the case of OSD failure or cluster rebalancing, Ceph can move or replicate a placement group and its contents, which means a Ceph Storage cluster can rebalance and recover efficiently.
  • The default placement group count that director creates is not always optimal, so it is important to calculate the correct placement group count according to your requirements. You can use the placement group calculator to calculate the correct count. To use the PG calculator, enter the predicted storage usage per service as a percentage, as well as other properties about your Ceph cluster, such as the number OSDs. The calculator returns the optimal number of PGs per pool. For more information, see Placement Groups (PGs) per Pool Calculator.
  • Auto-scaling is an alternative way to manage placement groups. With the auto-scale feature, you set the expected Ceph Storage requirements per service as a percentage instead of a specific number of placement groups. Ceph automatically scales placement groups based on how the cluster is used. For more information, see Auto-scaling placement groups in the Red Hat Ceph Storage Strategies Guide.


  • 64-bit x86 processor with support for the Intel 64 or AMD64 CPU extensions.

Network Interface Cards

  • A minimum of one 1 Gbps Network Interface Cards (NICs), although Red Hat recommends that you use at least two NICs in a production environment. Use additional NICs for bonded interfaces or to delegate tagged VLAN traffic. Use a 10 Gbps interface for storage nodes, especially if you want to create a Red Hat OpenStack Platform (RHOSP) environment that serves a high volume of traffic.

Power management

  • Each Controller node requires a supported power management interface, such as Intelligent Platform Management Interface (IPMI) functionality on the motherboard of the server.

1.3. Additional resources

The /usr/share/openstack-tripleo-heat-templates/environments/ceph-ansible/ceph-ansible.yaml environment file instructs the director to use playbooks derived from the ceph-ansible project. These playbooks are installed in /usr/share/ceph-ansible/ of the undercloud. In particular, the following file contains all the default settings that the playbooks apply:

  • /usr/share/ceph-ansible/group_vars/all.yml.sample

Although ceph-ansible uses playbooks to deploy containerized Ceph Storage, do not edit these files to customize your deployment. Instead, use heat environment files to override the defaults set by these playbooks. If you edit the ceph-ansible playbooks directly, your deployment fails.

For information about the default settings applied by director for containerized Ceph Storage, see the heat templates in /usr/share/openstack-tripleo-heat-templates/deployment/ceph-ansible.


Reading these templates requires a deeper understanding of how environment files and heat templates work in director. See Understanding Heat Templates and Environment Files for reference.

For more information about containerized services in RHOSP, see Configuring a basic overcloud with the CLI tools in the Director Installation and Usage guide.

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