Every synchronization mode in detail

O&O AutoBackup offers five modes in the pair wizard. Backup is included beside the synchronization modes so you can choose the desired outcome in one place.

Backup — keep every version

Idea: Copy new and changed files from left to right while preserving history. Nothing at the destination is deleted merely because it disappeared from the source. A changed file becomes another date-stamped version.

Ideal scenario: Maximum protection for documents, photos, and projects when recovery matters more than keeping the destination visually identical to the source.

Outcome: The destination grows into a versioned history. You can restore deleted files and earlier copies through O&O AutoBackup. Managed retention thins old history and prevents unrestricted growth.

Challenge: It requires the most destination space over time. It is not intended as an everyday working folder because older versions are part of the backup structure.

Copy — add and update, never remove

Idea: Copy new and changed files from left to right. A changed file replaces the older destination copy; the replaced item is sent to the Recycle Bin. Deleting a file on the left does not delete it on the right.

Ideal scenario: Maintaining a convenient secondary collection that should accumulate source files, such as copying exports to a review folder or adding new media to a library.

Outcome: The right side contains current copies of files still present on the left plus older right-side files whose source was deleted. There is no O&O AutoBackup version history.

Challenge: The destination can collect stale files because source deletions never clean it. Replaced files depend on the Recycle Bin rather than managed backup retention.

Merge — combine both folders, never delete

Idea: Copy new and changed files in both directions until each side contains the combined set. Deletions are not propagated.

Ideal scenario: Bringing together two incomplete collections without losing files—for example, merging photo folders from two PCs before organizing them.

Outcome: Both folders contain the union of the two starting sets. A file deleted from one side but still present on the other is copied back.

Challenge: Merge cannot be used to tidy a folder by deletion because the other copy resurrects the file. If the same file changed differently on both sides, the configured conflict policy decides the result.

Mirror — make the right folder an exact replica

Idea: Treat the left folder as authoritative. New files, changes, renames, and deletions are carried from left to right so the right side matches the left.

Ideal scenario: Publishing a prepared folder to a replaceable destination, maintaining a ready replica, or updating a device whose content should be exactly the same as the master folder.

Outcome: After a successful run, the right folder is an exact current copy of the left. Extra right-side items are removed, normally through the Recycle Bin.

Challenge: A mistaken deletion on the left is intentionally propagated. A unique file placed only on the right is considered unwanted and can be removed. Mirror has no version history of its own.

Two-way — keep both folders in step

Idea: Apply new files, edits, renames, and deletions from either side to the other. Both locations are treated as active working folders.

Ideal scenario: Working alternately from two locations, such as a desktop folder and a portable drive, when both sides may legitimately change.

Outcome: Both folders converge to the same current state. If one side deleted a file since the previous run, the deletion is carried to the other. If both sides changed the same file, the conflict policy is applied.

Challenge: This is the most demanding mode to reason about. An unwanted edit or deletion can travel both ways, and clock differences can affect a “newest wins” decision. Always inspect the preview and keep a separate versioned backup.

Comparison at a glance

Mode	Direction	Propagates deletion?	O&O AutoBackup version history?	Final intention
Backup	Left → Right	No	Yes	Recoverable history
Copy	Left → Right	No	No	Add/update collection
Merge	Left ↔ Right	No	No	Union of both folders
Mirror	Left → Right	Yes	No	Right exactly matches left
Two-way	Left ↔ Right	Yes	No	Both current folders match

“No deletion” does not mean “backup”

Copy and Merge avoid propagated deletions, but changed files do not receive O&O AutoBackup's managed version history. Use Backup when you need dependable earlier versions.