# Duplicacy — Lock-Free Deduplication Cloud Backup

> A new generation cloud backup tool featuring lock-free deduplication that supports over 30 cloud storage backends and allows multiple computers to back up to the same storage simultaneously.

## Install

Save in your project root:

# Duplicacy — Lock-Free Deduplication Cloud Backup

## Quick Use
```bash
# Download the CLI binary from GitHub releases
duplicacy init mybackup s3://mybucket@us-east-1/backups
duplicacy backup
duplicacy list
duplicacy restore -r 1
```

## Introduction
Duplicacy is a cross-platform backup tool that uses lock-free deduplication to allow multiple machines to share the same cloud storage without conflicts. Unlike traditional backup tools, it requires no central server — each client backs up independently while still deduplicating data across all clients.

## What Duplicacy Does
- Deduplicates data at the chunk level across multiple machines sharing the same storage
- Backs up to 30+ cloud storage backends including S3, Backblaze B2, Azure, GCS, SFTP, and local disks
- Uses lock-free design so multiple clients can back up simultaneously without coordination
- Encrypts all data client-side with AES-256-GCM before uploading
- Supports incremental backups with configurable retention policies and pruning

## Architecture Overview
Duplicacy splits files into variable-length chunks using a rolling hash, then deduplicates by content hash. Chunks are uploaded to the chosen storage backend individually. A snapshot file records which chunks compose each backup revision. The lock-free design avoids centralized locking by using optimistic concurrency — each client reads the latest snapshot index, uploads new chunks, and appends its snapshot. Conflicts are resolved by chunk-level content addressing.

## Self-Hosting & Configuration
- Download the single CLI binary (Go, no dependencies) for Linux, macOS, or Windows
- Initialize a repository with `duplicacy init <snapshot-id> <storage-url>`
- Configure encryption, chunk size, and threading in the `.duplicacy/preferences` file
- Schedule backups via cron or systemd timers on Linux, Task Scheduler on Windows
- Use the optional Web GUI (commercial license) for managing multiple repositories and schedules

## Key Features
- Lock-free deduplication allows concurrent backups from multiple machines to one storage
- Variable-length chunking provides high deduplication ratios across file modifications
- Client-side AES-256-GCM encryption with optional RSA key wrapping
- Supports backup copy to a secondary storage for 3-2-1 strategy
- Fast restore with parallel chunk downloads and in-place file reconstruction

## Comparison with Similar Tools
- **Restic** — Similar chunk-based dedup but uses repository locking; single-repo-per-machine is simpler
- **BorgBackup** — Mature dedup backup with compression; requires SSH access to the backup server
- **Kopia** — Modern backup tool with snapshot-based dedup; strong encryption, growing ecosystem
- **Duplicati** — GUI-friendly backup to cloud; uses block-level dedup but can be slower on large datasets
- **rclone** — Cloud sync tool without deduplication; good for mirroring but not incremental backup

## FAQ
**Q: Is Duplicacy free?**
A: The CLI is open source (personal use). The Web GUI requires a commercial license for non-personal use.

**Q: Can two computers back up to the same S3 bucket?**
A: Yes. Each computer uses a unique snapshot ID. Duplicacy deduplicates common data across all snapshots without coordination locks.

**Q: How do I prune old backups?**
A: Use `duplicacy prune -keep 30:180 -keep 7:30 -keep 1:7` to define retention tiers by age.

**Q: Does it support compression?**
A: Yes. Enable zstd or lz4 compression per chunk during initialization with `-compression-level`.

## Sources
- https://github.com/gilbertchen/duplicacy
- https://duplicacy.com

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Source: https://tokrepo.com/en/workflows/asset-fdbb39a1
Author: AI Open Source