Achieving Quorum in a Two Node Proxmox Cluster

Achieving Quorum in a Two Node Proxmox Cluster

In a Proxmox VE cluster, quorum is the minimum number of nodes that must be online and able to communicate with each other to make coordinated decisions and safely manage shared resources.

🔍 What Quorum Means in Proxmox

- Proxmox uses Corosync for cluster communication.
- Quorum ensures data consistency and split-brain prevention (where two nodes might think they own the same resource).
- Without quorum, the cluster disables key operations, such as starting or migrating VMs, to avoid corruption.

🧮 How Quorum Is Calculated

Quorum is based on the number of nodes in your cluster:
Quorum = (Total number of nodes / 2) + 1

In this video, we will maintain quorum by:
Editing the Configuration File:
- cp /etc/pve/corosync.conf /etc/pve/corosync.new.conf
- nano /etc/pve/corosync.new.conf
- Increase quorum votes to 2
- Increment the config version key in the totem section by 1
- mv /etc/pve/corosync.conf /etc/pve/corosync.conf.bak
- mv /etc/pve/corosync.new.conf /etc/pve/corosync.conf

If you really mess things up, it’s possible that the nodes won’t quorate. If this happens, the entire Proxmox cluster filesystem becomes read-only. You can temporarily reduce the required quorum to 1 to continue:
- pvecm expected 1.
⚠️ Important Notes:

- Two-node clusters are problematic without special configuration because you need both online at all times.
- To solve this, you can add a QDevice (a third quorum vote provider that doesn’t run VMs) or use external qnetd.
- Loss of quorum = “no quorum” status → cluster operations restricted (you may still force actions manually, but it's risky).

✅ Best Practices:

- Always have at least 3 nodes or 2 nodes + QDevice.
- Use redundant networking to prevent quorum loss from NIC failure.
- Avoid forcing actions when there's no quorum unless you fully understand the risk.

Links:
https://pve.proxmox.com/pve-docs/pve-admin-guide.html#_corosync_configuration

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Видео Achieving Quorum in a Two Node Proxmox Cluster канала Liv4IT