Erasure Coding (EC) is a popular method in Ceph for improving storage efficiency by splitting data into smaller chunks with parity for fault tolerance. However, the number of nodes in your Ceph cluster plays a critical role in its reliability. While smaller setups may look attractive for cost savings, they often compromise data redundancy, fault tolerance, and recovery speed.

Below, we break down why 3-node and 4-node Ceph clusters are not recommended for EC, and why a minimum of 5 nodes is ideal.

Why 3-Node Ceph Clusters Are Not Recommended for Erasure Coding

1. Lack of Redundancy

  • A typical EC configuration requires at least k+m chunks (data + parity) to work properly.
  • With only 3 nodes, all chunks (both data and parity) are forced to be stored across those same nodes.
  • This means if any single node fails, the cluster risks data loss or unavailability.
  • Unlike replication (where a full copy of data exists on another node), EC splits data into fragments—making small clusters highly vulnerable.

2. Inability to Maintain Quorum & Rebuild Data

  • Ceph depends on a quorum of MON (monitor) nodes for cluster stability.
  • In a 3-node setup, even one node failure can break quorum, potentially causing a total cluster outage.
  • Erasure coding also requires enough healthy nodes for data recovery—with only 3 nodes, there’s no spare capacity to handle rebuilds, leading to slow recovery times or even permanent data loss.

Why 4-Node Ceph Clusters Are Still Risky

1. EC Needs More Nodes for True Fault Tolerance

  • Common EC profiles like 2+2 (two data + two parity) require 4 nodes at minimum.
  • But if one node fails in a 4-node cluster, the system operates at critical risk because all nodes are fully utilised.
  • Recovery is slow and puts heavy strain on remaining nodes, which can further impact cluster performance.

2. Lack of Multi-Failure Protection

  • A 4-node EC cluster can only survive one node failure before losing data availability.
  • Since EC doesn’t store full copies of objects like replication does, there’s no safety net if another node goes down during recovery—making it unreliable for production.

Why 5+ Node Ceph Clusters Are Recommended

1. Better Redundancy & Fault Tolerance

  • With 5 nodes, you can configure EC profiles like 3+2 (three data + two parity), ensuring data remains accessible even if two nodes fail.
  • This reduces downtime and improves cluster stability for mission-critical workloads.

2. Faster Recovery & Balanced Load Distribution

  • More nodes allow Ceph to rebuild lost chunks faster by spreading the recovery load across the cluster.
  • This prevents performance bottlenecks during recovery and boosts overall IOPS and storage efficiency.

Conclusion

While 3-node or 4-node Ceph setups may seem cost-effective, they introduce serious risks such as data loss, long rebuild times, and unstable cluster operations. For a production-ready Ceph Erasure Coding environment, a minimum of 5 nodes is strongly recommended—offering better redundancy, higher fault tolerance, and improved performance.

At ServerAdminz, we specialize in Ceph cluster design, Erasure Coding setup, and performance optimization to ensure your storage infrastructure is both efficient and resilient.