The bytes DuoBolt shows you equal what your disk frees
Most duplicate finders count logical file sizes. On macOS, that's a lie: files copied with cp, snapshotted by Time Machine, or cached by build tools share storage at the filesystem level — deleting one of them frees nothing. DuoBolt detects these clone groups and counts each shared chain once, so every number in the app reflects what your drive actually recovers rather than what naïve arithmetic suggests.
Why naïve duplicate counts are wrong on APFS
When macOS copies a file on the same APFS volume, it doesn't duplicate the contents on disk — it creates a second directory entry pointing at the same physical blocks. Time Machine local snapshots, Apple Photos library imports, video editing project caches, Xcode's DerivedData, and most modern build tools rely on this. The result: your filesystem honestly reports three copies of a 609.77 MiB video, but every one of them shares the same blocks on disk. A less-honest duplicate finder would tell you 'recoverable: 1.79 GiB' and the number would be fiction. DuoBolt walks the APFS clone metadata directly, identifies which files share storage, and excludes that storage from the recoverable total. The group reports '0 B recoverable · 1.79 GiB total'. The dashboard's Total Wasted Space header reads 8.21 MiB instead of nearly 1.8 GiB, because 1.79 GiB of those duplicates aren't real bytes on disk. Selection size, the Review screen total, and the delete confirmation all read from the same clone-aware accounting — so the bytes you see before clicking Delete match what your disk will actually free.
Honest selection size
Tick clones for deletion and the bottom toolbar shows the bytes your disk will actually free — not file size × count. Tick eleven cloned files and the toolbar reads '4.6 GiB selected · 0 B reclaimable', because that is what your disk will do.
Group-level transparency
Groups with shared APFS storage display "X recoverable · Y total" in the header. You see at a glance which duplicates will free space and which are bookkeeping copies of bytes you've already counted.
Detected at scan time
Clone groups are identified during the scan itself by reading APFS inode metadata directly. No second pass, no UI guesswork — the recoverable number is final the moment the scan finishes.
macOS-only, zero overhead elsewhere
Clone detection runs on APFS volumes by default. On Windows, HFS+, or SMB shares it's a no-op — behavior is identical to any other scan. Switch it off per scan under Customize… → Scan parameters → Performance options.
How clone-aware accounting works
Four stages between the scan finishing and the recoverable number you see. The first is the ordinary duplicate pipeline; the next three are what clone awareness adds on top of it.
- Step
Group duplicates as usual
DuoBolt walks your scan roots and groups duplicates by full BLAKE3 hash — the same exact, byte-for-byte matching as any other DuoBolt scan.
- Step
Read APFS clone metadata
For each duplicate group on an APFS volume, DuoBolt asks the filesystem which files share physical storage. This is metadata, not content — milliseconds, not megabytes.
- Step
Compute recoverable per group
Each shared-storage chain counts only once toward the group's recoverable total. The "total" still reflects the logical sizes you'd see in Finder, so both numbers are available when you need them.
- Step
Propagate to every UI surface
Selection size, the Review screen total, the Total Wasted Space header, and the delete confirmation all read from the same clone-aware accounting. Nowhere in the app will you see an inflated number.
APFS clone detection FAQ
- What is an APFS clone?
- When you copy a file in Finder or with `cp` on the same APFS volume, macOS doesn't duplicate the bytes on disk — it creates a second directory entry that points at the same physical blocks. Both files are real and independent (editing one creates a new copy on disk), but until then they share storage. Time Machine local snapshots, Xcode's DerivedData caches, and many build tools rely on the same trick. How DuoBolt detects clones, and where it cannot →
- Why does my disk fill up if duplicate finders find gigabytes to recover?
- Because most duplicate finders count logical file sizes, not blocks on disk. Take the scan above: 136 GiB of duplicate files across 39,501 groups. A naïve tool would offer you 136 GiB back. DuoBolt's header says 1.9 GiB reclaimable, and the group list shows why — clone group after clone group reporting 0 B recoverable beside totals north of 700 MiB. Those are Logic Pro sample libraries that macOS cloned rather than copied; deleting one of each pair frees nothing at all. Tick eleven of them and the footer is blunt about it: 4.6 GiB selected, 0 B reclaimable. The first number is what your disk will actually give back. The second is what arithmetic on file sizes suggests.
- Does clone detection slow down scans?
- No measurable impact. The clone check is a per-group metadata lookup against APFS — milliseconds across a typical scan. The expensive work (reading and hashing file contents) is unaffected. Scans take the same time with it on or off, within run-to-run variance.
- What happens on Windows or non-APFS volumes?
- Clone detection is a no-op. DuoBolt reports a single 'total' number per group. There is no APFS equivalent on NTFS, ext4, HFS+, or SMB shares, so nothing to detect. Cross-platform behavior is unchanged.
- Can I turn clone detection off?
- Yes, per scan. Open Customize… on the scan setup screen, then Scan parameters → Performance options, and untick 'Detect APFS clones'. It is on by default, and most people have no reason to turn it off: when a volume has no clones the feature is invisible and every number is the plain one. Every scan parameter and its default →
- Why don't other duplicate finders detect APFS clones?
- It requires reading inode-level filesystem metadata that most cross-platform engines don't touch, plus a willingness to report two different numbers per group instead of one. Consumer duplicate cleaners optimize for a single satisfying 'X GB recovered' headline.
Keep exploring
Duplicate finder for Mac
The four macOS facts other duplicate finders get wrong: clone-aware totals, library folders it knows to skip, iPhone formats it opens by itself, and a Universal notarized build.
Read moreExact duplicate file finder
Why DuoBolt only flags byte-for-byte matches — and why exact matching is the foundation that makes clone-aware accounting trustworthy in the first place.
Read moreThe same thing, documented
How clone identifiers are read from the filesystem, what a 0 B group means, and the volumes where DuoBolt cannot tell — so the figure becomes an upper estimate.
Read more