When building a high-availability virtualization environment, one of the biggest challenges is creating reliable, redundant, and scalable storage — without the expense of dedicated SAN or NAS systems.
That’s where Proxmox VE and Ceph come together beautifully.

In this post, we’ll explore how Ceph storage works in a 3-node Proxmox VE cluster configured with 3 replicas, explaining the architecture, data distribution, and fault tolerance in practical terms.

What Is Ceph and Why Use It with Proxmox VE?

Ceph is an open-source, distributed storage system designed for high availability and self-healing. It provides block, object, and file storage across multiple servers, turning local disks into a unified and fault-tolerant storage pool.

Proxmox VE natively integrates Ceph, making it easy to build a hyperconverged infrastructure (HCI) — where every node contributes both compute and storage resources. This eliminates the need for external storage and simplifies cluster management.

1. Cluster Architecture Overview

In a 3-node Proxmox + Ceph cluster, each server (node) typically runs:

• Proxmox VE for virtualization
• Ceph MON (Monitor) – keeps track of cluster health and metadata
• Ceph MGR (Manager) – provides dashboard and management tools
• Ceph OSDs (Object Storage Daemons) – store the actual data blocks on local disks
• Optionally, Ceph MDS – used if you deploy CephFS for file-based storage

All three nodes are connected via high-speed networks and form a shared storage pool that any node can access.
Your virtual machines (VMs) can run on any node — and their disks live safely on the distributed Ceph storage.

2. What “3 Replicas” Actually Means

In Ceph, data is divided into small objects, and each object is stored multiple times across different disks or nodes based on a replication factor.

If you configure 3 replicas, Ceph ensures that:

Every object is stored three times — ideally once on each node.

So, if your VM writes 1 GB of data, Ceph will distribute three identical copies across the cluster.
This provides strong redundancy and fault tolerance.

3. How Data Is Distributed Across Nodes

Ceph doesn’t rely on a central storage controller. Instead, it uses an algorithm called CRUSH (Controlled Replication Under Scalable Hashing) to determine where to place each object.

When data is written:

1. Ceph splits it into small objects.
2. The CRUSH map calculates which OSDs (disks) should hold each object and its replicas.
3. Ceph writes and synchronizes the replicas across different nodes automatically.

This approach ensures:

• Even data distribution,
• High fault tolerance,
• Automatic recovery in case of hardware failure.

4. Example of Data Replication

Let’s say your VM writes 1 GB of data (called Data A). Ceph breaks it into smaller objects (e.g., 256 objects × 4 MB each). For each object, Ceph keeps three replicas — one on each node.

Ceph automatically spreads these replicas across all nodes and disks for balance and fault tolerance.

5. Fault Tolerance and Recovery

In a 3-node, 3-replica Ceph cluster:

• You can tolerate one node failure without data loss.
• The cluster continues to operate in degraded mode until the failed node returns.
• Once it comes back, Ceph automatically rebalances and restores the missing replicas.

If two nodes fail simultaneously, the cluster loses quorum and becomes read-only to protect data integrity — but no corruption occurs.

6. How Networking Impacts Ceph Performance

Because Ceph constantly replicates and synchronizes data between nodes, network performance is critical.

For best results:

• Use two dedicated networks:
  • Public network – used by Proxmox and client VMs.
  • Cluster (Ceph) network – used for replication and OSD traffic.
• Each should ideally be 10 Gbps or faster with low latency.

This separation ensures that VM traffic doesn’t interfere with Ceph replication.

7. Ceph and Proxmox Integration

One of Proxmox VE’s biggest advantages is its built-in Ceph integration.
From the Proxmox web interface, you can:

• Create Ceph monitors, managers, and OSDs
• Configure storage pools and replication levels
• Deploy CephFS or RBD (block storage)
• Monitor performance and health through a GUI

VM disks stored on a Ceph pool are automatically replicated and distributed — no manual configuration or external storage setup is required.

8. What Happens When a Node Fails

Let’s say Node 3 fails due to a power issue:

• The cluster detects the missing OSDs.
• Remaining nodes (Node 1 and Node 2) still have valid copies of all data.
• The cluster status changes to “Degraded”, but your VMs continue to run normally.
• Once Node 3 comes back online, Ceph:
  • Detects it automatically,
  • Resynchronizes the missing data,
  • Restores redundancy and returns to a “Healthy” state.

This self-healing mechanism is what makes Ceph so reliable in production.

9. Benefits of a 3-Node, 3-Replica Setup

High Availability – Data and compute redundancy protect against hardware failure.
Self-Healing – Automatic recovery and data rebalancing.
No Shared Storage – Each node contributes local disks; no SAN needed.
Scalable – Add more nodes or disks anytime.
Native Integration – Managed entirely within Proxmox VE.

10. Quick Reference Table

Conclusion

A 3-node Proxmox VE cluster with Ceph 3x replication is one of the most reliable and flexible ways to build high-availability virtualization infrastructure using open-source technologies.

You get:

• Enterprise-grade redundancy,
• Automatic self-repair, and
• Simplified management — all without expensive external storage systems.

For small to mid-size data centers, labs, or edge deployments, this architecture delivers a rock-solid balance of performance, resilience, and simplicity.