Full vs Incremental vs Differential: definitions, pros & cons, and when to use each

Selecting the right backup strategy is one of the most effective ways to reduce risk, control storage costs, and speed up recovery. This guide explains the main backup types, their advantages, disadvantages, and when to use each.

TL;DR Comparison

Definition: A full backup is a complete copy of selected data at a point in time. An incremental backup copies only changes since the last backup of any type. A differential backup copies all changes since the last full backup.

What is a Full Backup?

A full backup creates a complete, self-contained copy of the chosen data set, files, folders or entire systems, at a specific point in time. Because it copies everything, it is the most resource-intensive option but delivers the simplest, fastest recovery because a single backup set is sufficient to restore.

Advantages

• Simplest to understand and restore (one set).
• Clean, verifiable baseline for later backups and audits.
• Useful for monthly/quarterly images and compliance checkpoints.

Disadvantages

• Long backup windows; heavy bandwidth and I/O.
• Highest storage consumption.
• Impractical to run very frequently for large estates.

When to use

• Establishing baselines before switching to partial backups.
• Periodic “gold images” for disaster recovery and compliance.
• Workloads with rapid churn where partials won’t help.

What is an Incremental Backup?

An incremental backup saves only the data changed since the most recent backup, full or incremental. This minimises backup windows and storage by capturing smaller sets of changes. Restores require the last full backup plus every subsequent incremental taken up to the recovery point, which can make recovery slower.

How it works

• Day 0 (Sun): Full backup.
• Day 1 (Mon): Incremental of changes since Sun.
• Day 2 (Tue): Incremental of changes since Mon.
• Repeat until the next full (or synthetic full) resets the chain.

Pros

• Smallest daily backup size; fastest to run.
• Lowest bandwidth impact, ideal for remote sites.
• Cost‑efficient at scale.

Cons

• Restore depends on a chain: last full + all incrementals.
• Any missing or corrupted link increases recovery time or risks failure.
• Chain management and verification required.

Variations of Incremental Backups

• Regular incremental: Standard changes since the last backup of any type.
• Synthetic full: Builds a fresh full backup on the backup target by merging the last full with subsequent incrementals—no source re‑read.
• Incremental‑forever (progressive incremental): Take one initial full, then only incrementals; the platform synthesizes restore‑ready fulls on demand.
• Reverse incremental: Each new incremental is applied to the full on the target to keep an always‑current full; previous states remain as reverse deltas.
• Forever‑forward incremental: Maintain a single full; periodically merge the oldest incremental into the full and discard per retention.

Granularity options

• Block‑level incrementals: Copy only changed storage blocks inside files—more efficient when large files change slightly.
• Byte‑level incrementals: Even finer granularity for minimal change rates; smallest possible backups, higher processing needs.

When to use

• Tight backup windows and limited bandwidth.
• High change frequency where daily fulls are unrealistic.
• Cloud‑first or branch locations where network resources are limited.

What is a Differential Backup?

A differential backup captures all data changed since the last full backup. Each new differential is cumulative, so backup size grows until the next full. Restores are faster than incremental because you only need two sets: the last full plus the latest differential.

How it works

• Day 0 (Sun): Full backup.
• Day 1 (Mon): Differential of changes since Sun.
• Day 2 (Tue): Differential of changes since Sun (includes Mon changes).
• Grows daily until a new full resets size.

Pros

• Faster, simpler restores (two sets only).
• Lower risk from missing links compared to long incremental chains.
• Predictable recovery behaviour.

Cons

• Backups grow larger each day until the next full.
• Heavier on storage and bandwidth than incrementals.
• Windows expand during the cycle.

When to use

• Environments prioritising low recovery time over daily backup speed.
• Businesses where storage is affordable but downtime is costly.
• Periodic fulls (e.g., weekly) with daily differentials.

Incremental vs Differential: What’s the Difference?

The difference is the comparison point. Incremental copies only changes since the last backup of any type, producing the smallest daily backups but the longest restores. Differential copies all changes since the last full, creating larger daily backups but faster, simpler restores (last full + latest differential).

At a glance

• Backup window: Incremental shortest → Differential medium.
• Storage growth: Incremental lowest → Differential grows daily.
• Restore steps: Incremental many → Differential two.
• Risk of chain break: Incremental higher → Differential lower.

Choosing the Right Strategy (Scenarios & Schedules)

Start with objectives

• Recovery time objective (RTO): How quickly must systems be restored?
• Recovery point objective (RPO): How much data loss is acceptable?
• Constraints: Bandwidth, storage budget, change rate, compliance.

Common patterns

• Weekly full + daily incrementals: Balance of speed and storage.
• Weekly synthetic full + daily incrementals: Avoids re‑reading sources; keeps restores efficient.
• Weekly full + daily differentials: Slightly larger backups; faster recovery.
• Incremental‑forever + periodic verification: Smallest daily footprint; platform synthesises fulls on demand.

Retention & hygiene

• Align with policy (e.g., 30/90/365 days) and legal holds.
• Verify chains and perform regular test restores.
• Apply deduplication, compression and immutability where available.
• Follow the 3‑2‑1 (or 3‑2‑1‑1‑0) rule: 3 copies, 2 media, 1 off‑site, 1 immutable/air‑gapped, 0 verified errors after testing.

Best Practices Checklist

• Label backup sets consistently to avoid confusion during restores.
• Use application‑aware backups for databases and virtual machines.
• Schedule backups during low‑activity periods to minimise disruption.
• Encrypt data in flight and at rest; enforce MFA and role‑based access.
• Monitor change rates to adjust schedules effectively.
• Track cloud egress costs when planning restores.
• Document and rehearse recovery runbooks; measure actual RTO and RPO.

FAQs

Which backup is fastest to run? Incremental, because it captures only changes since the last backup of any type.

Which backup restores fastest? Differential (last full + latest differential), then full; long incremental chains are slowest.

Do I still need full backups? Yes. Fulls establish clean baselines for restores, verification and compliance—even with synthetic or incremental‑forever approaches.

Incremental vs differential for cloud? Incremental usually wins on cost and bandwidth; differential can be better when restore speed and simplicity matter most.

How often should I run a full backup? Commonly weekly, but synthetic fulls or incremental‑forever can reduce source impact while keeping recovery simple.