vSAN Capacity Calculator
Calculate usable vSAN capacity across OSA and ESA architectures. Models Adaptive RAID-5 (auto 2+1 ↔ 4+1), per-architecture policy availability, and Reserved Capacity (Operations Reserve + Host Rebuild Reserve).
OSA / ESA
Adaptive RAID-5 (2+1 / 4+1)
RAID-1 / 5 / 6
FTT 1 / 2 / 3
Reserved Capacity
Compression / Dedup
Your data stays on your device. All calculations run entirely in your browser — no data is sent to any VirtualBytes server.
Disclaimer: Capacity figures are estimates based on standard vSAN overhead formulas. Actual usable capacity varies based on compression efficiency, CLOM/metadata overhead, performance leg components (ESA), object size, and workload characteristics. Always validate against the official vSAN ReadyNode Sizer before procurement.
OSAOriginal Storage
ESAExpress Storage
Fault domains ?
None (host-based)
3 domains
4 domains
5 domains
6 domains
7 domains
Capacity disk size
960 GB SSD/NVMe
1.92 TB SSD/NVMe
3.84 TB SSD/NVMe
7.68 TB SSD/NVMe
15.36 TB SSD/NVMe
1 TB HDD (hybrid)
2 TB HDD (hybrid)
4 TB HDD (hybrid)
8 TB HDD (hybrid)
12 TB HDD (hybrid)
Device size ?
1.6 TB NVMe
1.92 TB NVMe
3.2 TB NVMe
3.84 TB NVMe
6.4 TB NVMe
7.68 TB NVMe
15.36 TB NVMe
30.72 TB NVMe
Dedup + compression ?
1:1 (none / disabled)
1.25:1 (light)
1.5:1 (typical compression)
2:1 (good — typical OSA D&C)
2.5:1 (excellent)
3:1 (exceptional)
4:1 (best case)
OSA: cluster-level dedup & compression. ESA: compression-only (no dedup) — per-object.
Reserved Capacity
Legacy slack
Operations Reserve
Headroom for resync, rebalance, policy changes (~5%)
Host Rebuild Reserve
Reserve ≈ 1 host worth of capacity for failure rebuild. Disable on 4-host clusters with ESA Auto-Policy.
Total reserve scales with cluster size — e.g. ≈ 25% on 4 hosts down to ≈ 8% on 12+ hosts (HRR ≈ 1/N + OR ≈ 5%).
Slack space ?
10%
20%
25% (recommended legacy)
30%
40%
Legacy fixed-percent model. Modern vSAN uses Reserved Capacity instead.
No calculation yet
Configure your cluster on the left and click Calculate.