Sync folders on Windows without deleting anything

Most “sync” horror stories have one cause: a mirror that removed files because they were missing on the other side. Here is how to copy only what is new or changed and leave everything else alone.

Why files disappear

A mirror makes the target identical to the source. That includes removing every file in the target that the source does not have. That is exactly what you want for a clean copy, and exactly what you do not want if the target also holds files that exist nowhere else. A non-deleting sync only adds and updates.

Option 1: robocopy, without /MIR

Windows includes robocopy. The switch /MIR (and /PURGE) deletes extra files in the target. Leave both out and nothing in the target is deleted:

robocopy "C:\Source" "D:\Target" /E /L

/E includes subfolders, /L only lists what would be copied, without copying. Run it once with /L, read the list, then run it again without /L. Add /XO if files in the target that are newer should not be overwritten by older ones.

Option 2: Folvane, with a preview

1. Choose both folders and press F5 to compare.
2. Pick “Update right” (or left). It copies new and changed files to the other side and removes nothing.
3. Check the action list. Every action is shown before anything happens, and single items can be unticked.
4. Confirm. Files that get overwritten are backed up first (in the hidden folder .folvane-backup), and the last sync can be undone in the history.

If changes happen on both sides, two-way sync copies the newer file in each direction. It does not delete, and when both sides changed it leaves the file alone instead of guessing.

Honest limits

• “Without deleting” does not mean “without overwriting”: an older file in the target is replaced by a newer one from the source. In Folvane that is previewed and backed up; with robocopy, check the /L list first.
• Because nothing is deleted, a file you removed in the source stays in the target. Both folders slowly drift apart in that direction. Use a mirror only when you want deletions carried over.
• Folvane syncs when you start it. It is not a background service.

Frequently asked questions

Does “Update right” in Folvane delete files?

No. It copies new and changed files to the right folder and removes nothing. Overwritten files are backed up first.

Does two-way sync carry over deletions?

No, on purpose. Without a stored previous state that would be guesswork. Use “Mirror” if deletions should be carried over; it is always previewed and backed up.

Can I undo a sync?

Yes. Overwritten and removed files are backed up beforehand, and the last sync can be undone in the history.

Does robocopy delete files?

Only with switches such as /MIR or /PURGE. Without them it copies and updates but leaves extra files in the target alone.

Folvane

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