Duplicates

How identical files are found, and why one copy is always kept.

How they are found

Among the largest files of each scanned location, files of the same size are sampled at the start, middle and end, hashed with SHA-256, then compared byte by byte. Only identical contents are grouped. Progress is shown by bytes read.

Keeping one copy

Each group keeps one copy. Stage the Rest for Review stages the others; the kept copy is never moved by group actions, and cleanup refuses the last copy of any group.

Identical is not the same

Two identical files can mean different things to different apps. Check where each copy lives before removing it.

Cloned files

APFS clones share blocks until one copy changes. Two clones are identical contents but removing one frees little. Redundancy is reported in logical bytes for this reason.

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