How to Add External Ceph RBD as Storage in Proxmox VE 9

In my previous posts,

This post is the next step: take that external Ceph cluster and hook it directly into Proxmox so you can place Proxmox VM/CT disks on Ceph RBD.

We will:

• Create a dedicated RBD pool for Proxmox.
• Create a CephX client user with access only to that pool.
• Add that pool as RBD storage in Proxmox VE 9 (web UI only).
• Create a test VM whose disk lives on Ceph RBD.

No extra packages are needed on Proxmox; all configuration is done in the web interface.

Lab Overview

My current lab:

• KVM host (physical)
  • OS: Ubuntu 24.04
  • Hypervisor: KVM/libvirt + Cockpit
  • Bridge: br0
  • Host IP: 192.168.0.84/24
• Proxmox VM (nested)
  • OS: Proxmox VE 9
  • Hostname: pve
  • IP: 192.168.0.11/24
  • Installed from proxmox-ve_9.0-1.iso
• Ceph node
  • OS: Ubuntu 24.04
  • Ceph: Squid v19 via cephadm
  • Hostname: ceph.maksonlee.com
  • IP: 192.168.0.81/24
• Existing Proxmox storages
  • local (Directory): backups, ISOs, container templates
  • local-lvm (LVM-Thin): VM/CT disks on the Proxmox VM’s virt disk
  • cephfs-pve (CephFS): shared backup/import/ISO/snippets storage

Goal:

Add an RBD pool named proxmox on the Ceph node, and a Proxmox storage named ceph-rbd that points to that pool and is used for VM/CT disks.

RBD in Proxmox is only for disks (VM and container). ISO images, templates, and backups should stay on directory/NFS/CephFS storage.

1. Create the proxmox RBD Pool (Ceph Node)

SSH into the Ceph node as administrator:

ssh administrator@ceph.maksonlee.com

Create a new pool named proxmox:

sudo cephadm shell -- \
  ceph osd pool create proxmox 8

Example output:

pool 'proxmox' created

Enable the RBD application on that pool:

sudo cephadm shell -- \
  ceph osd pool application enable proxmox rbd

Example:

enabled application 'rbd' on pool 'proxmox'

Initialize the pool for RBD:

sudo cephadm shell -- \
  rbd pool init proxmox

That’s enough to make proxmox a valid RBD pool for our VM disks.

2. Create a CephX User for Proxmox

Still on the Ceph node, create a dedicated client user that Proxmox will use to access the pool:

sudo cephadm shell -- \
  ceph auth get-or-create client.proxmox \
    mon 'allow r' \
    osd 'allow rwx pool=proxmox'

Example output:

[client.proxmox]
        key = AQDsgBppwICuFxAA/EwZ13V0DTNExrq18alqJQ==

Now display the full auth record:

sudo cephadm shell -- \
  ceph auth get client.proxmox

You should see something like:

[client.proxmox]
        key = AQDsgBppwICuFxAA/EwZ13V0DTNExrq18alqJQ==
        caps mon = "allow r"
        caps osd = "allow rwx pool=proxmox"

Copy this entire block; we’ll paste it into Proxmox in the next step.

3. Add Ceph RBD Storage in Proxmox (Web UI)

Open the Proxmox web interface:

https://192.168.0.11:8006/

Log in as root (Realm: Linux PAM standard authentication).

• View existing storages

• Open “Add RBD”

• Fill in the RBD fields

• Verify that ceph-rbd is active

From the Proxmox shell you can also run:

pvesm status

Name              Type     Status           Total            Used       Available        %
ceph-rbd           rbd     active        56565192               0        56565192    0.00%
cephfs-pve      cephfs     active        59699200         3137536        56561664    5.26%
local              dir     active        25654272         3478332        20847404   13.56%
local-lvm      lvmthin     active        18575360               0        18575360    0.00%

The important part is that ceph-rbd is active and shows the correct size and free space from the Ceph pool.

4. Create a Test VM with Disk on Ceph RBD

Now we’ll confirm the integration by creating a VM whose disk lives on ceph-rbd.

• Start the VM creation wizard

• OS tab – boot ISO from CephFS

• System tab – leave defaults

• Disks tab – place disk on ceph-rbd

• Confirm and create

• Boot the VM and start the installer

• Verify the RBD image on the Ceph node

sudo cephadm shell -- rbd ls proxmox

vm-100-disk-0

• Verify in the Ceph Dashboard