Deduplication: Skip, Overwrite, or Keep Both

Deduplication is a destination setting. It decides what Blober does when the exact destination path it is about to write is already occupied.

Deduplication compares the full destination path: destination folder, path template, and filename. Two files are duplicates when they would land on the same path.

It does not compare file contents. Nothing is hashed or read back from the destination to make this decision.

Policy	What happens	Where it is available
Skip if a file with the same name exists	The file is not written. Blober records it as skipped and continues with the next file.	Every destination that supports deduplication. This is the default.
Overwrite the existing file	The file at the destination is replaced.	Destinations that can replace a file in place.
Keep both (rename the new copy)	The new file is saved as name (1).ext, then name (2).ext, and so on.	Local destinations only.

Open the workflow, select the destination, and look for Deduplication in the destination configuration. The choice is saved with the workflow, so it applies to every run of that workflow.

The control only appears for destinations that can act on an existing file. Two cases have no setting:

• Source-only providers. A provider that can only be read from has nothing to deduplicate.
• Destinations with no reliable way to check whether a name already exists.

There is also one destination-specific rule:

Two different files can share a filename. Cameras, phones, and shared folders produce IMG_0001.JPG again and again, and Google Photos libraries commonly contain unrelated files with identical names.

Skip by name keeps one file per exact destination path. If your source can contain different files with the same name, either keep both or separate them with folder and path-template rules.

These solve different problems, and you can use both:

Situation	What handles it
A task was paused, cancelled, or interrupted by a crash or restart	Resume the same task. It keeps per-file progress and does not process records it already completed.
You deliberately want to run the workflow again	Deduplication decides whether files that are already at the destination get transferred again.

Resuming needs no setting and works on every provider. Deduplication is a per-destination choice and is limited to the providers listed above.

A rerun enumerates the source again and considers every file it finds. On a destination with deduplication, the setting is what stops the repeats:

• With Skip if a file with the same name exists, files already at the destination are skipped and the run only transfers what is missing. This is the setting to use for a repeat export into the same folder.
• With Overwrite the existing file, the destination copies are replaced on providers that support it.
• On a destination without deduplication, a rerun transfers the files again.

For a worked example with a long Google Photos export, read How Blober Handles Duplicate Files in Long-Running Backups.

Every cloud destination that supports deduplication uses the same two policies, skip and overwrite. Two providers document extra rules:

• Local adds the keep-both policy
• Azure Blob Storage always skips archived blobs

The option control in the app is the source of truth for a given destination: if the destination does not support deduplication, the control is not shown.