Answer the deletion question first
The most important difference is not the label: it is whether files found only in the target should remain or be removed.
Choose how your backup handles extras
FreeFileSync Mirror vs Update: keep backup extras safe
FreeFileSync Update preserves files removed from the source instead of deleting their backup copies. Mirror makes the target match the source, including deletions. Choose from the result you need, then inspect your synchronization and deletion settings before running either variant.
FileLever is available now on macOS. Windows and Linux builds of FileLever are planned. Your files stay under your control.
Quick answer
What is the difference between FreeFileSync Update and Mirror?
Choose Update when target-only files must stay, which is usually safer for a backup or archive. Choose Mirror only when the target should become a reviewed replica of the source.
| What happens | Update | Mirror |
|---|---|---|
| New or changed source files | Copied or updated in the target. | Copied or updated in the target. |
| Files found only in the target | Kept in place. | Can be removed so the target matches the source. |
| Best fit | Backups and archives that may contain deliberate extras. | A target you intentionally want to replicate the source exactly. |
Example: an older export exists only in your backup
Suppose the left folder is today's project and the right folder is its backup. You previously synced old-export.mov, then removed it from the left folder to make room. This is an illustrative example, not a captured FreeFileSync run.
| File | Update | Mirror |
|---|---|---|
| old-export.mov — removed from the source since the earlier sync | Retains the backup copy. | Deletes it from the target to match the source. |
| new-shot.jpg — newly added to the source | Adds it to the backup. | Adds it to the target. |
Check deletion handling and sync history too
FreeFileSync documents database-based change detection: Update can respect a deliberate deletion on the backup side rather than copying that file again. Custom rules also affect the plan. Read the configured actions instead of assuming every right-only or missing file has the same history.
Keeping target-only files does not preserve every older edit of a file that gets replaced. FreeFileSync offers Versioning to retain deleted or overwritten files separately; configure deletion handling before relying on it for recovery.
Want a reviewed backup workflow on Mac?
FileLever is a separate Mac app with its own copy/update and mirror workflow. Its preview separates proposed updates, target-only files, and unchanged files. The FileLever video below demonstrates that workflow; it does not show FreeFileSync settings or imply identical behavior between the apps.
Update keeps target-only files; Mirror can remove them after review.
Use Update for backups and archives that may legitimately contain extras.
Use Mirror only when the target should be an intentional replica of the source.
A deliberate workflow
A clear path from review to action
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Decide whether target-only files should stay
That is the mode decision. If target-only files are old exports, archive material, or anything you might still need, do not treat them as noise—use the preview to review them first.
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Choose Update for a conservative backup-style result
Use Update when the target should receive missing source files and changed versions but may legitimately contain extra files of its own. This is the safer default for a backup or archive.
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Choose Mirror only for an intentional replica
Use Mirror when the target is meant to match the source. In FreeFileSync, review the planned actions and deletion handling first. Do not assume that deletion order or confirmation steps are identical to FileLever's workflow.
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Verify the preview before you run either mode
Check new files, changed files, unchanged files, and target-only files. If the preview does not match your mental model of the two folders, stop and correct the folder pair or exclusions first.
Reduce sync mistakes
A visible preview makes it easier to spot an archive, export, or older file that should not disappear from the target.
Choose from the intended outcome
The right mode is the one whose result you can explain clearly before files move—not the one that sounds more thorough.
Product walkthrough
See the separate FileLever sync workflow
This FileLever recording shows its Mac sync preview and copy/update versus mirror choice. It is not a FreeFileSync tutorial; use the official FreeFileSync settings linked above for that app.
Common questions
Before you start
What is the difference between FreeFileSync Update and Mirror?
Update preserves backup copies when files are removed from the source. Mirror makes the target match the source, including deletions. Database history, custom rules, and deletion handling affect the configured actions, so inspect the plan before running it.
Does FreeFileSync Mirror delete files?
Mirror can remove files that exist only in the target because its goal is to make the target match the source. Review target-only files before confirming a mirror run.
Does FreeFileSync Update delete target-only files?
The Update variant does not propagate source deletions to the backup. Check your configured rules and database history rather than assuming every missing file will be copied again.
FreeFileSync update vs mirror — which is safer?
Update is usually safer for backups and archives because it preserves target-only files. Mirror is only safer when you intentionally want a reviewed replica and have already checked every target-only file.
When should I use Mirror instead of Update?
Use Mirror only when the target should become an exact replica of the source and you have already reviewed the target-only files carefully.
Is FileLever a FreeFileSync alternative for Mac?
Yes. FileLever is free to download on macOS and makes copy/update versus mirror an explicit, preview-first choice so you can protect backup extras before any sync runs. See the FreeFileSync alternative comparison for a side-by-side view.
See the files first. Decide what happens next.
FileLever is available now on macOS, with Windows and Linux planned.