Ceph Storage Capacity Calculator

Projected Usable Capacity

{{ formatCap(rawEffectiveTB) }} {{ unit }} Raw (post-overhead) {{ protectionLabel }} {{ (100 * totalEfficiency).toFixed(1) }} % Protected Eff.

Total nodes:

Capacity per node:

Define each node manually (heterogeneous):

Per-node capacities:

Node {{ i }}

Filled: {{ manualValidCount }} / {{ Math.max(0, Math.floor(Number(nodeCount) || 0)) }} nodes, {{ formatCap(rawTB) }} {{ unit }} total (before overhead).

Data protection:

OSD nearfull ratio :

{{ (nearfull * 100).toFixed(0) }} %

Failure domain for headroom :

OSDs / node

Cap {{ unit }}

Domains to tolerate (fail) :

OSD/metadata overhead :

{{ (osdOverhead*100).toFixed(1) }} %

CRUSH imbalance skew :

{{ (skew*100).toFixed(1) }} %

Accept degraded PGs (override recommended nearfull) :

Recommended nearfull ≤ {{ (recommendedNearfull * 100).toFixed(0) }}% to recover after {{ failNodes }} {{ failureDomain }} failure{{ failNodes===1?'':'s' }}. Using {{ (effectiveNearfull * 100).toFixed(0) }}%.

Metric	Value	Copy
Nodes	{{ nodes.length }}
Raw storage ({{ unit }})	{{ formatCap(rawTB) }}
Overhead ({{ unit }})	{{ formatCap(rawTB - rawEffectiveTB) }}
Raw post-overhead ({{ unit }})	{{ formatCap(rawEffectiveTB) }}
OSD nearfull (used)	{{ (effectiveNearfull*100).toFixed(0) }} %
Recommended nearfull	{{ (recommendedNearfull*100).toFixed(0) }} %
Protection	{{ protectionLabel }}
Protected efficiency	{{ (100*totalEfficiency).toFixed(2) }} %
Efficiency @ min_size	{{ (100*minEfficiency).toFixed(2) }} %
Usable capacity ({{ unit }})	{{ formatCap(usableTB) }}
Redundancy overhead ({{ unit }})	{{ formatCap(redundantRawTB) }}
Reserved / free raw ({{ unit }})	{{ formatCap(reservedRawTB) }}

Tags: Devops , Networking , Storage , Sysadmin

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Ceph stores objects with redundancy so a cluster can lose devices or nodes and keep data available. Capacity planning balances raw storage with protection costs and a safe fill level that leaves headroom for recovery work.

Choose replication or erasure coding, set how many copies or data and parity chunks you need, and enter node capacities. Pick a nearfull threshold that leaves space to reshape data when failures happen. The calculator shows usable capacity, redundancy overhead, and reserved space.

Use a higher headroom when you tolerate multiple node losses in the same failure domain. Adding nodes increases raw storage while also improving balance, which can increase effective headroom at the same threshold.

The model simplifies placement and assumes balanced data across devices. Use it to compare protection modes and to set a safe nearfull level for your environment.

Technical Details

Raw capacity is the sum of node capacities after subtracting per‑OSD or filesystem overhead and any skew factor. Usable capacity depends on the protection scheme and the portion of raw space you allow the cluster to use before marking OSDs nearfull.

\begin{matrix} Raw & = & \sum_{nodes} C_{i} \\ Raw′ & = & Raw \times (1 - o) \times (1 - s) \\ Used raw & = & Raw′ \times f \\ Efficiency & = & rep: \frac{1}{r}, EC: \frac{k}{k + m} \\ Usable & = & Used raw \times Efficiency \end{matrix}

Symbols and units
Symbol	Meaning	Unit/Datatype	Source
Ci	Capacity of node i	TB	Input
o	Overhead fraction	0–0.95	Input
s	Skew fraction	0–0.95	Input
f	Nearfull fraction	0–1	Input/derived
r	Replica size	integer	Input
k, m	EC data, parity chunks	integers	Input

Worked example

Six nodes at 10 TB, replication size 3, nearfull 85, zero overhead and skew.

Raw = 6 \times 10 = 60 TB

Used raw = 60 \times 0.85 = 51 TB

Usable = 51 \times \frac{1}{3} \approx 17 TB

Raising nearfull leaves more free raw space but reduces immediately usable capacity. Erasure coding can improve efficiency at the cost of rebuild time.

Input & validation

Validation rules
Field	Type	Accepted values	Notes	Placeholder
Nodes	integer	≥ 0	Manual per‑node caps optional	6
Unit	enum	TB	Display only	TB
Mode	enum	rep \| ec	Replication or EC	rep
replicas	integer	≥ 1	Size for replication	3
ec k+m	integers	k ≥ 1, m ≥ 0	Chunks for EC	4+2
nearfull	number	0–1	Effective ≤ recommended	0.85
Overhead, skew	number	0–0.95	Applied multiplicatively	0
Failure domain	enum	host \| osd \| custom	Headroom estimate	host

I/O formats

Inputs and outputs
Input	Accepted Families	Output	Encoding/Precision
Node capacities, protection, thresholds	Numbers and enums	Raw, usable, redundancy, reserved	2 decimals
—	—	CSV/JSON exports	Plain CSV; UTF‑8 JSON

Privacy & compliance

All inputs are processed locally. No cluster information is transmitted.