How to estimate backup storage size

Quick answer: Start from your current data size, multiply by how many copies your retention keeps, apply compression (databases shrink 5–10×, media barely at all), and add 30% headroom plus growth. With incremental tools like restic or borg, long retention costs far less than the naive copies×size math suggests.

Overview

Sizing a Storage VPS is a five-minute calculation once you know three numbers: data volume, change rate, and retention. Overshoot a little — a backup target at 95% disk is a failing backup target.

Before you start

• Measure what you actually back up:

  du -sh /var/www /etc /home /var/backups

• Know your retention tiers and frequency.
• Estimate daily change rate — compare two days of incremental transfer logs, or assume 2–5% for typical sites.

Step-by-step guide

1. Baseline: one full copy = data size after compression. Example: 40 GB site + 5 GB database dump → ~25 GB compressed.
2. Mirror-style (rsync snapshots with hard links): full size + (daily change × days kept). 25 GB + (1 GB × 30) ≈ 55 GB.
3. Deduplicating tools (restic/borg): similar math but changes are block-level and compressed — real-world archives often need 1.2–2× the live size for months of history.
4. Add headroom: ×1.3 for safety, plus your 12-month growth guess (traffic up = uploads up).
5. Sanity-check quarterly:

   df -h /srv/backups

   and prune or upgrade before 80% fills.

Common issues

• Counting uncompressed dumps: SQL text compresses dramatically — measure the .gz, not the .sql.
• Forgetting logs and mail: /var/log and mailboxes grow quietly; include them or exclude them deliberately.
• No room for the restore drill: testing sometimes needs scratch space on the same box — headroom again.

When to contact support

Between two plan sizes, or expecting a data spike (migration, new project)? Ask in a ticket — upgrading a Storage VPS later is possible, but starting right is cheaper than an emergency move at 99% disk.

Frequently asked questions

How well do backups compress?

Text compresses superbly — SQL dumps often shrink 5–10 times with gzip. Photos, video and already-compressed archives barely shrink at all, so measure the compressed sizes.

How much extra space do deduplicating tools need?

restic and borg store changed blocks only, so months of history commonly fit in 1.2–2 times the live data size — far less than the copies-times-size math of full backups.

How much headroom should a backup disk keep?

Plan to stay under 80% full: add roughly 30% headroom to your estimate plus expected 12-month growth. A backup target with a full disk is a backup system that has already failed.

Related articles

• How to order a Storage VPS
• Backup retention policy explained
• How to check disk space
• How often should you back up your server?

Need reliable space for your backups? Order a Storage VPS at Cloud2Y →