Storage Manager

A fast, native disk-usage treemap for Apple Silicon Macs — WizTree-style boxes, built with a Rust scanning core and a SwiftUI front end.

Why it's fast

Most disk scanners issue one lstat syscall per file — for a million files, that's a million kernel round-trips. Storage Manager's Rust core uses getattrlistbulk(2), a macOS syscall that returns name, type, size, inode, and link count for a whole batch of directory entries at once, cutting syscalls by orders of magnitude. Directories are walked in parallel across all cores with rayon.

Measured on an M-series MacBook (12 cores, ~956k files, 296 GB home directory, warm cache):

Tool	Scan time
du -sk	22.7 s
naive parallel read_dir + lstat	3.5 s
Storage Manager	~2.2 s

(WizTree on Windows reads NTFS's Master File Table directly; APFS has no user-readable equivalent, so a filesystem walk is the floor on macOS — this is about as close to it as it gets.)

Accuracy

• Sizes are allocated on-disk bytes (ATTR_FILE_ALLOCSIZE), matching du byte-for-byte — sparse files, APFS clones, and compressed files are not overreported.
• Hardlinked files are counted once (deduped by device + inode).
• Symlinks are never followed and count as zero.
• Filesystem boundaries are respected; scanning / correctly handles macOS's firmlink-stitched System/Data volume split without double-counting.

Features

• Auto-populated drive picker (mounted volumes + home directory)
• Squarified-style treemap: box area ∝ size; click a folder to drill in, breadcrumb to climb back out
• Hover for exact sizes; right-click any box to Copy Path or Reveal in Finder
• Scan timing in the status bar

Architecture

scanner/            Rust static library
  src/lib.rs        getattrlistbulk walker, rayon parallelism,
                    C FFI: scan_path() -> JSON, free_string()
StorageManager/     Swift package
  Sources/CScanner/         C header + modulemap bridging the Rust lib
  Sources/StorageManager/   SwiftUI app: treemap layout + UI

The two halves talk over C FFI: Rust serializes the size tree to JSON and hands Swift a C string; Swift decodes it with Codable. Rust allocates, Rust frees.

Building

Requires Rust (any recent stable) and Xcode command-line tools.

cd scanner && cargo build --release
cd ../StorageManager && swift build -c release

The result is a single self-contained binary (the Rust lib is statically linked). To wrap it as an app bundle, see make-app.sh.

Full Disk Access

macOS blocks apps from reading most directories outside your home folder — no error, just silently missing data. For accurate full-drive scans, grant the app System Settings → Privacy & Security → Full Disk Access.

Testing

The Rust core has a test suite covering du parity (byte-exact), edge cases (unicode and JSON-hostile filenames, hardlinks, symlink loops, permission-denied directories, deep nesting, sparse files), scan determinism, and FFI leak stress:

cd scanner && cargo test --release -- --test-threads=1