How to Add External CephFS as Storage in Proxmox VE 9

In the previous post,

we already:

• Installed a single-node Ceph v19 cluster with cephadm
• Created a CephFS filesystem named cephfs
• Created a CephX client user client.cephfs
• Saved its key into /etc/ceph/client.cephfs.secret on the Ceph node

In this post, we’ll connect that existing CephFS to Proxmox VE 9 and use it as one of the storages.

Typical use cases for CephFS in Proxmox:

• ISO images
• LXC templates
• VZDump backups
• Snippets
• “Import” content for the VM Import wizard

CephFS is not for VM disks in Proxmox — use Ceph RBD for VM disks instead.

Lab Overview

• Ceph node
  • Hostname: ceph.maksonlee.com
  • IP: 192.168.0.81
  • Managed with cephadm
  • CephFS: cephfs
  • CephX user: client.cephfs
  • Secret file: /etc/ceph/client.cephfs.secret
• Proxmox node
  • Hostname: pve.maksonlee.com
  • IP: 192.168.0.11
  • Proxmox VE 9.0.3 (nested on KVM)
  • ceph-common is already installed by Proxmox (no manual apt install needed)

Goal:

Add cephfs as a CephFS storage named cephfs-pve in Proxmox, and upload an ISO image into it.

1. Confirm CephFS and the Client Key (Ceph Node)

On the Ceph node, we can confirm CephFS and see the key files:

sudo cephadm shell -- ceph fs ls

sudo cephadm shell -- ceph fs ls

name: cephfs, metadata pool: cephfs.cephfs.meta, data pools: [cephfs.cephfs.data ]

name: cephfs, metadata pool: cephfs.cephfs.meta, data pools: [cephfs.cephfs.data ]

sudo ls /etc/ceph/*

sudo ls /etc/ceph/*

/etc/ceph/ceph.client.admin.keyring  /etc/ceph/ceph.client.cephfs.keyring  \
/etc/ceph/ceph.conf  /etc/ceph/ceph.pub  /etc/ceph/client.cephfs.secret

/etc/ceph/ceph.client.admin.keyring  /etc/ceph/ceph.client.cephfs.keyring  \
/etc/ceph/ceph.conf  /etc/ceph/ceph.pub  /etc/ceph/client.cephfs.secret

We only need the raw key stored in client.cephfs.secret:

sudo cat /etc/ceph/client.cephfs.secret

sudo cat /etc/ceph/client.cephfs.secret

AQDCwBlp...redacted...==

AQDCwBlp...redacted...==

Copy that line somewhere safe. We’ll paste it into the Proxmox UI as the Secret Key.

2. Add CephFS Storage in the Proxmox Web UI

Open the Proxmox Web UI at:

https://pve.maksonlee.com:8006

In the left tree:

• Click Datacenter.
• Go to Datacenter → Storage.
• Click Add → CephFS.

Click Add.

Proxmox will:

• Create a cephfs: cephfs-pve entry in /etc/pve/storage.cfg
• Save your key into /etc/pve/priv/ceph/cephfs-pve.secret
• Mount CephFS under /mnt/pve/cephfs-pve on the node

3. Verify the New CephFS Storage

Back in the Proxmox tree you should now see:

• cephfs-pve (pve) listed as a storage, next to local and local-lvm

Click cephfs-pve and you’ll see tabs like:

4. Upload an ISO Image to CephFS

Now we’ll actually put something on this storage.

• In the left tree, click cephfs-pve → ISO Images.
• Click Upload.

You’ll see an upload dialog:

Choose your ISO file (for example ubuntu-24.04.2-live-server-amd64.iso) and click Upload.

Proxmox will:

• Temporarily store the upload in /var/tmp on the node
• Then move it into the CephFS path (e.g. /mnt/pve/cephfs-pve/template/iso/)

Make sure /var/tmp and the CephFS filesystem both have enough free space.

After the upload finishes, the ISO appears in the list: