Kopia is a cross-platform backup and restore tool designed for users who need fast, secure, and cost-efficient data protection without being locked into proprietary cloud services. It backs up individual files and directories—not full disk images—using client-side end-to-end encryption, data deduplication, and compression to minimize storage costs and bandwidth usage. Kopia is ideal for developers, sysadmins, and power users who want full control over where their data is stored.
Built in Go, Kopia supports multiple storage backends including Amazon S3, Azure Blob Storage, Google Cloud Storage, Backblaze B2, WebDAV, SFTP, and Rclone-compatible services. It provides both a command-line interface for automation and a desktop GUI for ease of use. Kopia repositories can be hosted locally, on network-attached storage, or on a dedicated Kopia Repository Server, enabling centralized backup management across multiple machines.
What You Get
- Client-side end-to-end encryption - All data is encrypted on the client before upload using AES-256, with user-controlled keys; no one—including the storage provider—can access your unencrypted data.
- Data deduplication - Only unique file blocks are stored, reducing storage usage by up to 90% for repetitive data like VM images or versioned files.
- Compression support - Files are compressed using LZ4 or Zstandard before encryption, reducing storage and bandwidth requirements.
- Multi-cloud and local storage support - Back up to S3, Azure Blob, GCS, Backblaze B2, WebDAV, SFTP, Rclone (Dropbox, OneDrive, Google Drive), or local filesystems.
- Command-line and GUI interfaces - Full-featured CLI for scripting and automation, plus a native desktop GUI for Windows, macOS, and Linux with visual snapshot management.
- Error correction and data integrity - Uses Reed-Solomon erasure coding to detect and repair corrupted or missing data blocks in the backup repository.
Common Use Cases
- Backing up home directories across multiple devices - A user backs up their macOS, Windows, and Linux laptops to a single Google Cloud Storage bucket, leveraging deduplication to avoid redundant storage costs.
- Running a centralized backup server for a small business - An IT admin sets up a Kopia Repository Server on a local NAS to collect encrypted backups from 10 employee workstations without relying on third-party SaaS.
- Archiving large media libraries to low-cost cloud storage - A photographer uses Kopia with Backblaze B2 to store 5TB of raw photo files with deduplication, reducing monthly storage costs by 70%.
- Automating backups in DevOps pipelines - A developer configures Kopia via CLI to back up critical configuration files and database dumps after each CI/CD deployment to an S3 bucket with versioned retention policies.
Under The Hood
Architecture
- Clear separation of concerns through modular Go packages, with distinct layers for CLI, repository logic, and filesystem abstractions enabling independent testing and reuse.
- Dependency injection via constructor-based interfaces decouples core services from concrete implementations, supporting flexible backend substitution.
- Plugin-like extensibility for blob storage backends follows the Strategy pattern, allowing new cloud or local storage providers to be added without modifying core logic.
- Electron-based UI is cleanly separated from the CLI backend, communicating via inter-process communication while sharing the same repository engine.
- Build and testing infrastructure enforces architectural boundaries using build tags, static analysis, and coverage thresholds to maintain modularity and platform-aware deployment.
Tech Stack
- Go (1.20+) serves as the foundation, leveraging standard library packages for filesystem, cryptography, and concurrency with high performance.
- Build and release pipelines use Makefile, GoReleaser, and GitHub Actions to produce cross-platform binaries with full ARM64 and AMD64 support.
- Static analysis tools enforce logging standards, ban vendor-specific SDKs in favor of minio-go, and restrict time package usage for consistency.
- Code quality is maintained through comprehensive test suites, license compliance checks, and automated packaging for Debian/RPM distributions.
- Deployment includes embedded Electron UI, native cloud storage integrations, and end-to-end testing via Playwright for UI reliability.
Code Quality
- Extensive test coverage spans unit, integration, and end-to-end scenarios with clear layer separation and reusable test utilities.
- Robust error handling uses typed custom errors and structured stack traces for precise debugging and user-facing clarity.
- Strong type safety and well-defined interfaces ensure data integrity and reduce runtime surprises across snapshotting and metadata systems.
- Idiomatic Go naming conventions and package boundaries enhance readability and maintainability across the codebase.
- Automated testing environments abstract setup complexity, ensuring reliable and reproducible test execution across platforms.
What Makes It Unique
- Integrates a high-performance, content-addressed storage engine with native filesystem semantics, enabling deduplicated backups that appear as regular directories while preserving cryptographic integrity.
- Unifies snapshotting, block-level deduplication, and client-side encryption into a single repository format, eliminating reliance on external tools like rsync or tar.
- Delivers a seamless desktop GUI built atop Electron that directly interfaces with the CLI’s core engine, removing the need for separate backend services or APIs.
- Implements client-side key management for cloud storage backends, ensuring data privacy without vendor lock-in or centralized key storage.
- Introduces deterministic, tamper-proof snapshots with cryptographic audit trails at every layer, setting a new standard for verifiable backups in open-source tools.