Immutable Backup Storage Overhead Calculator

Translate retention policies into hard storage requirements for immutable backups. Provide the baseline protected data set and the number of months you must preserve snapshots to see total capacity needs, peak snapshot size, and the space savings impact of dedupe or compression.

Usable data volume captured by each full backup before dedupe.
How many immutable snapshots you must preserve.
Defaults to 3%. Represents net data expansion each month before dedupe.
Defaults to 1. Enter 0.72 for 28% space savings, 0.5 for 50% savings, etc.

Storage projections assume deterministic growth and constant dedupe. Validate against actual backup analytics and vendor sizing guides before purchasing capacity.

Examples

  • 22 TB baseline, 12-month retention, 3% monthly growth, 0.72 dedupe ⇒ Immutable storage required: 204.94 TB across 12 snapshots • Average protected data per month: 17.08 TB • Peak snapshot size after dedupe: 19.01 TB • Data growth over baseline: 37.43% • Dedupe/compression factor applied: 0.72×.
  • 48 TB baseline, 6-month retention, defaults for optional fields ⇒ Immutable storage required: 291.05 TB across 6 snapshots • Average protected data per month: 48.51 TB • Peak snapshot size after dedupe: 55.60 TB • Data growth over baseline: 15.93% • Dedupe/compression factor applied: 1.00×.

FAQ

How do I handle weekly or daily retention requirements?

Convert the schedule to an equivalent number of full monthly snapshots or run the calculator separately for each cadence and sum the outputs.

Can I model incremental backups?

Yes. Estimate the effective monthly growth rate by dividing incremental change volume by the full data set, then enter that percentage so the sum of snapshots matches your incremental policy.

What if dedupe varies over time?

Use the most conservative (highest) dedupe factor you have seen in production. For more precision, rerun the tool with multiple factors and compare the totals.

Does this include off-site replication copies?

No. Multiply the total storage requirement by the number of immutable replicas you plan to maintain to capture additional copies.

Additional Information

  • Snapshots are treated as full copies retained for the specified months; growth applies compounding to each successive copy.
  • Monthly growth accepts raw percentages (e.g., 3 or 3%) or decimal rates (e.g., 0.03).
  • Dedupe/compression factor multiplies the raw storage total. Enter 1 for no savings, a fraction for space reduction, or a value above 1 to model overhead.
  • Use the output to size immutable object storage, air-gapped appliances, or WORM-capable cloud tiers before committing to retention SLAs.

Related calculators