SAN Sizing Calculator

About the SAN Sizing Calculator

Sizing a Storage Area Network (SAN) requires accounting for far more than just current data volumes. Snapshots, replication, data growth, thin provisioning overhead, and spare capacity all consume space that must be planned for. Under-sizing leads to emergency expansions at premium prices, while over-sizing wastes capital on shelf-ware.

This calculator models SAN capacity over time by combining your usable storage requirements with growth projections, snapshot retention, and replication overhead. Enter your current usable capacity, annual growth rate, snapshot policy, and replication needs, and get a multi-year capacity forecast. Use the results to time your hardware refresh cycles and negotiate volume pricing with storage vendors.

When This Page Helps

SAN hardware has long lead times and significant procurement cycles. This calculator gives you the data to justify purchases, time expansions, and avoid costly emergency orders by projecting capacity needs years into the future.

How to Use the Inputs

1. Enter your current usable capacity requirement in TB.
2. Enter the expected annual growth rate as a percentage.
3. Enter the number of years to project.
4. Enter the snapshot overhead as a percentage of usable space.
5. Enter the replication multiplier (1 = no replication, 2 = one replica).
6. Review the projected total capacity needed.

Example Calculation

Tips & Best Practices

• Plan for at least 3 years of growth to align with typical SAN hardware refresh cycles.
• Keep 15–20% headroom above projected needs for unexpected workloads.
• Thin provisioning saves initial capacity but monitor overcommit ratios carefully.
• Snapshot space varies greatly by workload—10–30% is typical, but databases may need 50%+.
• Include deduplication and compression savings only if your SAN supports them natively.
• Factor in RAID overhead—RAID 6 uses ~30% of raw capacity for parity.

Multi-Year Capacity Planning

SAN hardware typically has a 3–5 year lifecycle. Plan your initial purchase to cover at least 3 years of projected growth, with expansion shelves available for years 4–5. This approach balances capital efficiency with operational flexibility.

The Impact of Data Reduction

Modern SANs with inline deduplication and compression can reduce physical capacity needs by 2–5× for general workloads and up to 10× for VDI environments. However, already-compressed data (images, video, encrypted data) sees minimal reduction. Size for the worst case and enjoy the savings.

Cloud-Connected SAN

Hybrid SAN solutions tier cold data to the cloud while keeping hot data on local flash. This can reduce on-premises capacity needs by 30–60% for workloads with significant cold data. Factor in cloud storage costs and retrieval latency when evaluating this option.

Frequently Asked Questions

• What annual growth rate should I estimate?

  Industry averages are 20–40% annually, but this varies widely. Measure your actual growth over the past 12 months for the best estimate. Data-intensive workloads (analytics, media) can grow 50%+ per year.

• How much space do snapshots use?

  Snapshot space depends on data change rate and retention. A snapshot of a 10 TB volume with 5% daily change retained for 7 days uses roughly 3.5 TB (5% × 10 × 7). Frequently changing databases consume more snapshot space.

• What is a replication multiplier?

  The multiplier accounts for copies of data for disaster recovery. A multiplier of 2 means one additional copy (source + replica). Synchronous replication to a DR site doubles your raw storage requirement.

• How does RAID affect total raw capacity?

  RAID 5 loses one disk per group to parity (~20–25% overhead). RAID 6 loses two disks (~30–35%). RAID 10 uses half the raw capacity. Divide usable capacity by the RAID efficiency to get raw disk requirements.

• Should I include thin provisioning in my estimates?

  Thin provisioning delays physical allocation, but the data will eventually be written. Plan for the full projected usage, not the thin-provisioned amount. Over-committing thin provisioning is a leading cause of SAN outages.

• When should I trigger a SAN expansion?

  Start the procurement process when utilization hits 70%. Most SAN expansions take 4–12 weeks from order to installation. By 80% utilization, performance may degrade. Never let a SAN exceed 85–90% utilization.