Kopia — Cross-Platform Backup Tool with Encryption, Compression, and a Polished UI

Introduction

Kopia is a newer, polished sibling to Borg and Restic. It focuses on friendly UX — including a desktop GUI (KopiaUI) and a web UI — while keeping the fundamentals: content-addressable storage, client-side encryption, compression, and snapshot-level policies. Native backends for S3/GCS/Azure/B2/WebDAV/SFTP avoid the rclone indirection other tools need.

With over 13,000 GitHub stars, Kopia is popular with users who want "Borg's reliability but with a UI my less-technical colleague can operate". It's cross-platform and runs identically on macOS, Linux, and Windows.

What Kopia Does

Kopia splits files into variable-size blocks (content-addressable), deduplicates across all snapshots in a repository, encrypts everything with ChaCha20+Poly1305 or AES-GCM, and optionally compresses. Policies (per path) control retention (keep N hourly/daily/weekly/monthly/annual). A repository server lets many client machines share a single dedup pool without giving them direct storage credentials.

Architecture Overview

[Client machine(s)]
      |
[Kopia binary — CLI + web UI]
   snapshot, policy, restore
      |
[Content-addressable storage layer]
   split into chunks, dedup, encrypt (AEAD)
   compress (zstd / s2 / pgzip / lz4)
      |
+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |
S3  GCS Azure B2 WebDAV SFTP FS RClone
      |
[Kopia Repository Server (optional)]
   client machines connect to the server,
   the server talks to storage
   per-user policies, bandwidth limits

Self-Hosting & Configuration

# Set a global policy
kopia policy set --global \
  --keep-latest 10 \
  --keep-hourly 24 --keep-daily 7 --keep-weekly 4 --keep-monthly 24 \
  --compression=zstd-better-compression \
  --add-ignore '*.log' --add-ignore 'node_modules'

# Per-directory override
kopia policy set /home/alice/projects \
  --add-ignore '.git' --add-ignore '.venv' --max-file-size 100M

# Repository server (multi-machine access without sharing storage creds)
kopia server start --tls-generate-cert --address 0.0.0.0:51515 \
  --server-username admin --server-password admin-pass

# Client machine
kopia repository connect server --url https://backup-server:51515 \
  --server-cert-fingerprint abcdef... --username alice --password ...

# Schedule (cron example)
0 * * * * kopia snapshot create /home/alice --quiet

# Web UI at http://localhost:51515 (or wherever server runs)
# KopiaUI desktop app bundles server + UI for solo users

Key Features

• Native cloud backends — S3, GCS, Azure, B2, WebDAV, SFTP, local, rclone
• Strong encryption — AEAD (ChaCha20-Poly1305 or AES-GCM-SIV)
• Compression — zstd, s2, pgzip, lz4; per-policy selection
• Content-addressable + dedup — same block stored once across snapshots/machines
• KopiaUI — polished desktop app for macOS/Linux/Windows
• Web UI — browser interface for repository servers
• Policy-based retention — hourly/daily/weekly/monthly/annual per path
• Cross-platform — binary for every major OS and arch

Comparison with Similar Tools

FAQ

Q: Kopia vs Borg vs Restic? A: All three are excellent. Borg is the veteran (fastest on some Linux workloads). Restic has cloud backends + simpler CLI. Kopia has cloud backends + GUI + multi-user repository server. For teams: Kopia. For servers with SSH-only targets: Borg. For script-centric cloud backups: Restic.

Q: How does Kopia compare on dedup efficiency? A: Very similar to Borg/Restic — content-defined chunking with a ~4MB average chunk. Dedup ratios of 5-10x are typical for full-system backups.

Q: Can I share one repository across many machines? A: Yes — that's one of Kopia's strengths. Use the Kopia Repository Server; each client authenticates with its own credentials; dedup spans everyone's data.

Q: Is KopiaUI as capable as the CLI? A: 90%+ for everyday use. For advanced policies or scripting, drop to the CLI. KopiaUI is a friendly wrapper — the same binary powers both.

Sources

• GitHub: https://github.com/kopia/kopia
• Website: https://kopia.io
• License: Apache-2.0