msy 0.4.1

Modern musl rsync alternative - Fast, parallel file synchronization

Quick Start

sy /source /destination

That's it. Use sy -h for help.

When to Use msy

msy excels at:

• Repeated local syncs — 2-3x faster after first run
• Large files on APFS/BTRFS/XFS — 40x+ faster via COW reflinks
• Many small files over SSH — 2x faster initial sync (5000+ files)
• Mixed workloads — 2x faster

rsync is better for:

• First-time local sync of small files — ~1.1x faster
• SSH incremental updates — ~1.3x faster

Bottom line:

• msy wins on local sync (especially repeated), COW filesystems, and large SSH transfers.
• rsync has slight edge on incremental SSH updates.

Installation

From crates.io

cargo install msy

Optional features

cargo install sy --features acl    # ACL preservation (Linux: requires libacl)
cargo install sy --features s3     # S3 support (experimental)

From Source

git clone https://github.com/pepa65/msy
cd msy
cargo install --path .

For SSH sync: Install msy on both local and remote machines.

Examples

# Basic
sy ~/project ~/backup                    # Local backup
sy ~/src ~/dest --delete                 # Mirror (remove extra files)
sy /source /dest --dry-run               # Preview changes

# Remote
sy /local user@host:/remote              # SSH sync
sy /local user@host:/backup --bwlimit 1MB

# Verification
sy ~/src ~/dest --verify                 # Verify writes (xxHash3)
sy ~/backup ~/original --verify-only     # Audit existing files

# Filters
sy ~/src ~/dest --exclude "*.log"
sy ~/src ~/dest --gitignore --exclude-vcs

# Advanced
sy --bidirectional /laptop /backup       # Two-way sync
sy ~/dev /backup --watch                 # Continuous sync
sy ~/src ~/dest -j 1                     # Sequential (many tiny files)

Trailing slash: msy follows rsync semantics — /source copies the directory, /source/ copies contents only.

Features

• Delta sync — Only transfers changed bytes (rsync algorithm)
• Parallel transfers — Configurable worker count (-j)
• Resume support — Automatically resumes interrupted syncs
• Integrity verification — Optional xxHash3 checksums (--verify)
• Bidirectional sync — Two-way sync with conflict resolution
• Watch mode — Continuous file monitoring
• SSH transport — Binary protocol, faster than SFTP for bulk transfers
• S3 support — AWS S3, Cloudflare R2, Backblaze B2 (experimental)
• Metadata preservation — Symlinks, permissions, xattrs, ACLs

Platform Support

Contributing

Contributions welcome! See CONTRIBUTING.md.

License

MIT — see LICENSE.