Frequently Asked Questions

 

What is diskDedupe?

diskDedupe will deduplicate files by replacing duplicate files with clones. The cloned files will keep all meta data of the replaced file, so modification time, creation time, links, aliases etc. will remain unchanged after deduplication.

Since clones use almost no space on the harddisk, the space of the duplicate file is reclaimed.

 

I ran diskDedupe, but it did not reclaim disk space. What happened?

diskDedupe measures the difference in available space before and after deduplication. There are three main reasons why no space is saved even when duplicates are detected:

1. Multiple runs: Running diskDedupe repeatedly won't save additional space as files are already cloned.

2. Finder copies: Files copied with Finder on the same volume are already space-efficient clones.

3. System snapshots: Space might be temporarily locked by macOS snapshots and will be freed after 1-2 days. Use this Terminal command to list all local snapshots:

tmutil listlocalsnapshots /

 

Why do I need APFS for diskDedupe?

diskDedupe needs a filesystem that supports cloning of files. APFS on the Apple Platform is currently the only file system that supports this feature. If you select a volume or directory that does not support cloning (e.g. Mac OS Extended), diskDedupe will not be able to clone files and therefore cannot reclaim any diskspace.

 

Why do some files create a warning message when opening them in Finder after deduplication with diskDedupe?

Apple's macOS creates those warning messages for files that were changed by an application downloaded from the Mac App Store. We applied for an exemption and have provided an app version for which the operating system does not create those error messages, but that version did not get approved by Apple.

We continue to work with Apple’s Developer Support and App Review Team to address this issue. In the mean time, you can use this short how-to to remove the warnings set by Apple for files deduplicated with diskDedupe:

1. Start Terminal
2. cd to the directory that you selected in diskDedupe for deduplication
3. Copy and paste the following code snippet into Terminal (one line)
xattr -rls . | grep ";diskDedupe" | sed -e 's/: com\.apple\.quarantine.*$//' | while read -r name; do xattr -d com.apple.quarantine "$name"; done
4. Execute the line by pressing Return

 

What happens if I modify a cloned file? Will the deduplicated (cloned) file also be modified?

You can modify any file after deduplication. Unlike hard links, cloned files can be modified separately.