diskDedupe FAQ

diskDedupe uses SHA-256 hash comparison of file content to identify exact duplicates. This guarantees the same security as byte-by-byte file comparison. File names, dates, and other metadata can differ - only the actual content needs to be identical.

Only APFS supports file cloning on Mac. APFS has been the standard file system on macOS since macOS 10.13 (2017), so most users are not affected by this limitation. diskDedupe will not work on HFS+ or other file systems.

No, diskDedupe is not supported on iCloud Drive. iCloud's unique storage behavior may retain both original and deduplicated files, potentially increasing storage use. diskDedupe automatically detects and skips iCloud files and folders.

APFS clones are a copy-on-write feature specific to Apple's APFS filesystem. Unlike hard links, aliases, or symbolic links, clones are completely transparent to the operating system and applications. They appear as independent files but share the same disk blocks until one is modified.

You can modify any file after deduplication. Unlike hard links, cloned files can be modified separately without affecting other clones. When a cloned file is modified, APFS allocates new storage for the changes, while the unmodified clone continues to share the original data blocks.

No, APFS cloning only works within a single volume. Clones cannot be created across different volumes, even within the same APFS container.

Performance varies based on drive type and data amount. Here are some examples for the first run; subsequent runs are much faster due to caching. With many large duplicates or spinning disks, it can take significantly longer:

• External 2TB SSD via Thunderbolt (95% full, 360GB duplicates): ~22 minutes
• 1TB internal SSD with 753GB data and only few duplicates: ~5 minutes
• Internal SSDs are generally faster than external drives

Yes, you can set minimum and maximum file size limits in Settings. This focuses deduplication on files where it provides the most benefit and significantly speeds up the process. Note that setting a minimum below 4KB is typically not recommended, as cloning very small files may not yield substantial space savings due to filesystem overhead.

diskDedupe is designed to preserve file integrity and excludes system files by default. However, always backup your data before running any deduplication tool.

If you have Time Machine backups configured, make sure it is up-to-date. For quick and safe testing, you can also use macOS's built-in snapshot feature. This works even if Time Machine is not configured:

• Use tmutil localsnapshot to create an instant backup of your entire drive. For example:

  sudo tmutil localsnapshot /

• Rename the snapshot in Disk Utility to prevent auto-deletion (see details below).
• Run your tests.
• If issues occur, restore files from the snapshot by mounting it as a read-only volume.

To mount and rename snapshots:

• Open Disk Utility.
• Click View > Show All Devices.
• Find your drive and expand it to see snapshots.
• Right-click a snapshot to:
  • Rename: Select "Rename Snapshot" and give it a descriptive name to prevent auto-deletion.
  • Mount: Select "Mount Snapshot".
• Don't forget to delete the snapshot in Disk Utility (right-click > Delete...) when no longer needed.

Note: Snapshots auto-delete after 12-24 hours unless renamed in Disk Utility.

No, focus on specific folders rather than scanning your entire system. System files and read-only areas are unlikely to have duplicates and may cause permission issues. Target user directories, external drives, or folders where you know duplicates exist.

While technically possible, use caution. Some applications may not expect their files to be cloned. Always backup these libraries first.

Space may be temporarily locked by snapshots and usually be freed within 1-2 days.

• Check for snapshots:

  tmutil listlocalsnapshots /

This is macOS's quarantine system flagging files created by sandboxed apps. The content isn't damaged. Remove quarantine flags with the following command in Terminal (run from the parent directory of affected files):

xattr -rls . | grep ";diskDedupe" | sed -e 's/: com\.apple\.quarantine.*$//' | while read -r name; do xattr -d com.apple.quarantine "$name"; done    

diskDedupe preserves creation and modification dates, but "Date Added" (maintained by Spotlight) may change because sandboxed apps cannot modify Spotlight data. Use "Date Modified" for sorting to maintain expected order.

You have two options:

• Create a Custom Category with the file extension you want to exclude. Then disable it for deduplication.
• Create a .diskDedupe.config file in your target folder. Use content like this:

[exclude]
excludeFolder1
excludeFile1

[original]
protectedFolder1
importantFile1

[system variables]
minimumFilesize = 1048576
maximumFilesize = 1073741824
cacheFile = off

• [exclude]: Files/folders to ignore completely.
• [original]: Files used only as source, never replaced.
• [system variables]: Override default settings.

The cache file (.dedupeCache) stores file hashes to speed up subsequent scans by only re-hashing changed files. You can disable caching in Settings if you prefer not to create hidden cache files or prefer to have a clean run.

Yes, since version 2.0, diskDedupe can detect existing APFS clones. It will skip these files during deduplication since they already share storage space. This prevents unnecessary re-cloning operations and makes the process more efficient.

Currently, diskDedupe is only available as a GUI application.

Contact support at [email protected]. The development team is responsive and often provides beta versions to help resolve specific issues.

Send reports to [email protected] including:

• macOS version
• diskDedupe version
• System specifications (RAM, drive type)
• Description of when the issue occurs
• Crash logs (found in ~/Library/Logs/DiagnosticReports)

Currently, there's no free trial version, though this is under consideration. You can return the app through the Mac App Store if it doesn't meet your needs.