Understanding GFS and How It Relates to Duplicati

GFS (Grandfather-Father-Son) is a hierarchical backup scheme:

• Son – frequent backups (e.g., daily)

• Father – less frequent backups (e.g., weekly)

• Grandfather – long-term backups (e.g., monthly or yearly)

The general idea is to keep many recent recovery points but fewer older ones. On common use of Duplicati’s Retention policy is to apply GFS logic through time-based rules.

Example from Duplicati docs:

7D:U,1Y:1W

Keeps all backups for 7 days, then one per week for up to a year.

Key Retention Options

Duplicati supports three modes:

• Delete older than – remove everything older than a set time.

• Keep versions – retain a fixed number of backups.

• Retention policy – rules that specify buckets

  Example: 1W:1D,4W:1W,12M:1M

  • Keep 1 per day for 1 week  

  • Keep 1 per week for 4 weeks  

  • Keep 1 per month for 12 months

Rules are applied from newest to oldest. Anything outside defined ranges is deleted. Duplicati always keeps at least one backup.

Building a GFS-Style Retention Policy

Step 1: Define Frequencies

Decide what GFS tiers mean in your context:

• Son = daily

• Father = weekly

• Grandfather = monthly or yearly

Step 2: Schedule Backups

Schedule daily backups. Duplicati’s retention logic automatically picks which backups remain per period so you don’t need to label them manually.

Step 3: Apply the Policy

Example GFS policy:

7D:U,4W:1W,12M:1M

Meaning:

• Keep all backups for the last 7 days  

• Keep 1 per week for 4 weeks  

• Keep 1 per month for 12 months  

Add yearly retention if desired:

7D:U,4W:1W,12M:1M,3Y:1Y

Now you’ll keep:

• Daily for a week  

• Weekly for a month  

• Monthly for a year  

• Yearly for 3 years  

Example Scenario

Our goal is to end up with keeping one backup:

• Daily for 14 days  

• Weekly for 8 weeks  

• Monthly for 24 months  

• Yearly for 5 years  

The retention policy that matches this would be:

14D:U,8W:1W,24M:1M,5Y:1Y

This ensures fine-grained recent backups and progressively fewer long-term copies.

Combining Rules

• Use Keep versions to enforce a minimum count.

• Use Delete older than to cap maximum age.

• Use Retention policy for structured GFS rotation.

Caveats

• Missed backups reduce available weekly/monthly points.  

• Space usage rises with short-term “unlimited” settings.  

• Duplicati deletes versions but storage reduction may happen later.

• Always test restores periodically.

Summary

Duplicati’s retention makes GFS simple: 7D:U,4W:1W,12M:1M,3Y:1Y.

You get:

• Many recent “sons”  

• Fewer “fathers”  

• Rare “grandfathers”  

This achieves efficient, tiered backup retention without manual rotation.

Ready to try out Duplicati? Head to the download page and get started!