Access the cluster using rbd client

Objective

This guide explains how to access your OVHcloud Ceph cluster from a machine configured as an RBD client. It describes how to prepare your environment, configure network access, and connect securely to your Cloud Disk Array.

Requirements

Before proceeding:

• A Cloud Disk Array solution
• Your client machine’s public or private IP is allowed in the Access Control List (ACL){} of your Ceph cluster. See our guide "Cloud Disk Array - IP ACL creation".
• You have the following credentials (available in the OVHcloud Control Panel):
• Cluster monitor IPs
• Ceph username (client.<username>)
• Secret key (keyring content)

Instructions

Installing Ceph on the client machine

For Debian/Ubuntu distributions:

sudo apt-get update
sudo apt-get -y install ceph ceph-common

For RHEL/CentOS distributions:

sudo yum install -y ceph-common

Retrieve connection details

Log in to the OVHcloud Control Panel, click Bare Metal Cloud, then Cloud Disk Array and select your service.

Overview:

• Locate the monitor IPs for your Ceph cluster.

Users:

• Find the Ceph username and key required for authentication.

Configure the client

Create or edit the file /etc/ceph/ceph.conf with the following content:

[global]
mon_host = <MONITOR_IP_1>:6789, <MONITOR_IP_2>:6789, <MONITOR_IP_3>:6789

Create a keyring file for your Ceph user at /etc/ceph/ceph.client.<username>.keyring:

[client.<username>]
key = <your_secret_key>

Ensure the keyring file has restricted permissions for security:

sudo chmod 600 /etc/ceph/ceph.client.<username>.keyring

Test the connection and configuration

Verify that the client can successfully connect to the Ceph cluster:

ceph -s --id <username>

If the configuration is correct, the command returns the current cluster status.

To validate the setup, list the images available in your pool:

rbd -n client.<username> list <pool_name>

An empty result indicates that no images have been created yet. If an error occurs, review the configuration files and credentials to ensure they are correct.

Create, map, and mount an RBD volume

A Ceph pool cannot be mounted directly. You must first create an RBD image within the pool and then map it to a block device.

Create an RBD image:

rbd -n client.<username> create <pool_name>/<image_name> \
  -s <size_in_MB> \
  --image-format 2 \
  --image-feature layering

Verify image creation:

rbd -n client.<username> list <pool_name>

Map the image to a block device:

sudo rbd -n client.<username> map <pool_name>/<image_name>

Verify the mapping:

rbd showmapped

Format the block device (XFS example):

sudo mkfs.xfs /dev/rbd0

Mount the filesystem:

sudo mkdir -p /mnt/<mount_point>
sudo mount /dev/rbd0 /mnt/<mount_point>
df -h /mnt/<mount_point>

You can now start using your Ceph block storage.

Unmount and unmap the RBD volume

Before detaching an RBD image, ensure the filesystem is properly unmounted:

sudo umount /mnt/<mount_point>
sudo rbd unmap /dev/rbd0

The RBD image is now safely detached from the client.

Notes and best practices

• Always use the monitor IP addresses provided in the OVHcloud Control Panel.
• Avoid storing sensitive information in plain-text configuration files.
• For Kubernetes environments, use the CSI RBD driver with the same configuration and credentials.

Go further

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