DiskManager

A native macOS app (SwiftUI) to compare, sync and clean up two storage locations — external drives, local folders, or any two folders. It was originally built to manage two external drives kept in different places (A: 8 TB, B: 10 TB) that only occasionally get plugged into the same Mac. The UI is bilingual (Traditional Chinese / English) and can be switched live from the toolbar.

Website · Download for Mac · Install guide

Download & install

1. Download the latest DiskManager-<version>.dmg from Releases, open it and drag DiskManager.app into Applications.

2. The app is not notarized by Apple, so Gatekeeper blocks it on first launch:

   • macOS 15 Sequoia and later: open the app once and dismiss the warning, then go to System Settings › Privacy & Security, scroll to Security and click Open Anyway.

   • macOS 14 Sonoma: in Finder, right-click the app › Open, then click Open.

   • Any version: remove the quarantine flag in Terminal:

     xattr -dr com.apple.quarantine /Applications/DiskManager.app
     

3. Enable DiskManager under System Settings › Privacy & Security › Full Disk Access (see Permissions below).

The website has the full step-by-step install guide.

Requirements: macOS 14 Sonoma or later, Apple Silicon. You can also build from source (see Building).

Sync tab

The layout has three rows, top to bottom: mode → target space A (the source of truth; never modified, highlighted with the accent color) → operated space B (the side that gets changed). For the opposite direction, press the "Swap" button between the two rows — existing scan results are reused, no rescan needed. That is why there are no mirrored duplicate modes such as B→A or A−B. In union mode both sides are equal and neither is highlighted.

Three modes (switch instantly; the plan is recomputed from cached scan results without rescanning):

Mode	Behavior
Mirror	Make operated space B match target space A (one-way mirror with A as the source of truth)
Difference	Preview only the items that exist in B but not in A, then archive them or move them to the Trash after confirmation; nothing is copied or overwritten
Union	Fill in missing files on both sides; when the same file differs, the one with the newer modification time wins and the overwritten version is archived first. Items whose age can't be determined, or that conflict in type, are left untouched and listed

In mirror mode, extra files on the operated space are handled as you choose: keep, move to archive folder (default), or move to Trash.

Changing folder A or B after a plan has been previewed invalidates the plan immediately; you must rescan before running it.

Preview

• Scanning and comparing are strictly read-only; you get the full plan before pressing "Start Sync".
• Tree diff list: expand and collapse folders like a file browser. Folders show aggregated size and +add / ~overwrite / !extra counts. Filter by action, and export the full list as JSON or plain text.
• Storage visualization: usage bars for both spaces (including the bytes this run will write — turns red and blocks the sync when space is insufficient), plus a size breakdown of the top-level folders in the scanned range.

Safety

• Nothing is ever deleted outright: extra or replaced files go to _DiskManager_Archive/<timestamp>/ by default.
• Atomic overwrites (temp file + rename), so cancelling mid-way never leaves a half-written file. Files locked in Finder are temporarily unlocked for the replace, then the flag is restored.
• Modification times and metadata are preserved; on exFAT it falls back to data + timestamps, with a 2-second tolerance when comparing times.
• Filename case is handled according to each side's file system, so Folder / folder are not treated as two different items on case-insensitive volumes.
• System sleep is prevented during scans and syncs; the toolbar also has a "Keep screen on" toggle.

Cleanup tab

Finds removable junk in a storage space. Everything is listed for you to check first; items go to the Trash by default, and permanent deletion needs an extra confirmation.

This is the beginning of the README. Read the rest at the original. Read the full README ↗