Ceph Storage Capacity in a 3-Node XXL v4 OpenMetal Cluster

Q: What is the usable Ceph storage capacity in a 3-node OpenMetal XXL v4 cluster?

A three-node OpenMetal XXL v4 Hosted Private Cloud cluster provides approximately 38.4TB of usable Ceph storage with 3x replication, or approximately 76.8TB with 4+2 erasure coding — from 115.2TB of raw NVMe across 18 drives.

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Each XXL v4 node contributes 6 × 6.4TB NVMe data drives (38.4TB raw per node). Pooled across three nodes: 115.2TB raw. With Ceph’s default 3x replication, usable capacity is 115.2 ÷ 3 = 38.4TB. With 4+2 erasure coding (4 data + 2 parity), efficiency is approximately 66.7%, yielding ~76.8TB usable.

3x replication is the default for clusters serving hot data — it provides higher write throughput, simpler recovery, and lower rebuild overhead after a drive or node event. 4+2 erasure coding suits warm or cold data tiers where storage efficiency matters more than peak write IOPS.

All 18 OSDs run on Micron 7500 MAX NVMe drives, so Ceph block volume latency is bounded by local NVMe performance rather than network-attached storage. The cluster is expandable beyond three nodes to increase both raw and usable capacity.