STOP - If You Are Using Mirror Mode, You Are Deleting Your Files - Switch to UPDATE Now - Here Is Exactly How
I lost thousands of files using Mirror mode in FreeFileSync. I am not a novice - I have decades of technology experience, including Novell NetWare network administration. I chose Mirror because in networking, "mirror" means redundancy and protection - keeping two locations identical by safely copying changes. It does NOT mean deleting files from your backup that no longer exist in your source. That is not what mirror means to anyone with a networking or systems background.
But that is exactly what FreeFileSync Mirror does. Every single time I ran it, it quietly deleted files from my backup destination. For months. I lost financial records, legal documents, including an active disability benefits appeal, medical records, and months of work on my book that I am currently publishing. The damage took an entire day to begin recovering from.
=== THE FIX - DO THIS RIGHT NOW ===
DO NOT left-click the Synchronize button - that will run Mirror immediately and delete your files.
Instead RIGHT-CLICK on the Synchronize button. A menu appears with three options:
- Two-Way
- Mirror
- Update <--- SELECT THIS ONE
Select UPDATE. That is it. Update copies new and changed files to your backup destination, but NEVER delete anything. Your backup files are always safe. This is what almost every user actually wants when setting up a backup.
After selecting Update - click Synchronize normally. Your files will be safely backed up without anything being deleted.
=== WHY THIS IS A CRITICAL UI FAILURE ===
1. The sync mode change requires a RIGHT-CLICK on the Synchronize button. There is no visible indication that right-clicking does anything different. This is completely non-discoverable. Most users will never find it.
2. A simple left-click runs the sync immediately in whatever mode is set - including the destructive Mirror mode - with no warning whatsoever.
3. There is no confirmation dialog before Mirror runs. A simple warning saying "Mirror will delete files from your backup that do not exist in your source - are you sure?" would save countless users from data loss.
4. The word Mirror is deeply misleading to anyone from a networking background, where mirror means safe redundant protection - not destructive deletion.
5. Mirror is the default. Update should be the default. Always.
I respectfully urge the FreeFileSync team to consider:
- Making the sync mode a visible, prominent dropdown - not a hidden right-click
- Adding a mandatory warning before Mirror runs
- Changing the default to Update
- Adding a red visual warning when Mirror is active
FreeFileSync is excellent software, and I will continue using it now that I understand it. But please - make the fix discoverable so the next person does not lose what I lost.
If this post saves even one person from data loss, it was worth writing.
Kerry Alan Royce
Retired Licensed Rehabilitation Counselor, M.S., LRC
Author, Swimming in the AcidStream: A Guidebook for People with Physical Disabilities
If You Are Using Mirror Mode You Are Deleting Your Files - Switch to UPDATE Now - Here Is Exactly How
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- Joined: 11 Jun 2019
The meaning of mirror has been debated for a long time and isn't clear-cut, as you stated above. A deletion is a change, so mirroring should propagate those as well according to your description. If you have decades in tech, why aren't you reading documentation, testing and practicing a more robust backup strategy? Sorry you lost data, but FFS itself includes versioning and Recycle Bin support.keeping two locations identical by safely copying changes. It does NOT mean deleting files from your backup that no longer exist in your source
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- Joined: 22 Aug 2012
As per the FreeFileSync Manual page on sync variants
> 1. The sync mode change requires a RIGHT-CLICK on the Synchronize button.
.... This is completely non-discoverable. Most users will never find it.
I don't know which version of FreeFileSync (FFS) you are using, and on what platform.
But the Synchronize button only shows the present sync mode/variant setting.
For changing that setting you must left click the green gear-icon, the Synchronize Settings button (F8), which gives access to all sync settings. Or by right clicking said green gear-icon, or left or right clicking the small right-pointing arrow, either of which (only) enables you to change the sync variant.
Clicking a gear-icon to change settings is pretty universal throughout the industry.
Besides that, it is written in the Basic Usage and Main Dialog Overview FFS Manual page.
> 5. Mirror is the default. Update should be the default. Always.
Two-way is the default, not Mirror, unless you changed that yourself.
On a side-note: Also in the Two-way variant, after the first sync, files you delete at one side will be deleted at the opposite side.
Particularly because you apparently have decades of technology experience in the field, it is quite surprising to see you did not:
• First familiarize yourself with the software you are using
(amongst other things, you would have noticed the cited Mirror variant description)
• First use test data, instead of critical data, to see if the results match your expectations
• First run a Compare before running an actual sync
The latter allows you to review proposed sync actions and verify if those match your expectations.
If so desired, you can then still modify your sync mode, modify individual sync actions and/or include and exclude files from the sync via the In- and Exclude Filter.
So, instead of urging users to not use the Mirror sync variant, it makes more sense to urge users to act in line with the three bullets just above, before committing to a sync on critical data.
Depending on a users needs, FFS's Mirror sync can be a very useful and powerful sync method.
But, whatever sync variant you are running: always make sure you know what you are doing.
Only for a properly developed and verified sync configuration directly click the Synchronize button.
The same holds for (silently) running sync configurations saved as a *.ffs_batch file, as those, just like when directly clicking the Synchronize button, do not pause between the Compare and Synchronize phase.
The (Mirror) synchronization will create and delete files on the target as needed until it is an exact copy of the source.
> 1. The sync mode change requires a RIGHT-CLICK on the Synchronize button.
.... This is completely non-discoverable. Most users will never find it.
I don't know which version of FreeFileSync (FFS) you are using, and on what platform.
But the Synchronize button only shows the present sync mode/variant setting.
For changing that setting you must left click the green gear-icon, the Synchronize Settings button (F8), which gives access to all sync settings. Or by right clicking said green gear-icon, or left or right clicking the small right-pointing arrow, either of which (only) enables you to change the sync variant.
Clicking a gear-icon to change settings is pretty universal throughout the industry.
Besides that, it is written in the Basic Usage and Main Dialog Overview FFS Manual page.
> 5. Mirror is the default. Update should be the default. Always.
Two-way is the default, not Mirror, unless you changed that yourself.
On a side-note: Also in the Two-way variant, after the first sync, files you delete at one side will be deleted at the opposite side.
Particularly because you apparently have decades of technology experience in the field, it is quite surprising to see you did not:
• First familiarize yourself with the software you are using
(amongst other things, you would have noticed the cited Mirror variant description)
• First use test data, instead of critical data, to see if the results match your expectations
• First run a Compare before running an actual sync
The latter allows you to review proposed sync actions and verify if those match your expectations.
If so desired, you can then still modify your sync mode, modify individual sync actions and/or include and exclude files from the sync via the In- and Exclude Filter.
So, instead of urging users to not use the Mirror sync variant, it makes more sense to urge users to act in line with the three bullets just above, before committing to a sync on critical data.
Depending on a users needs, FFS's Mirror sync can be a very useful and powerful sync method.
But, whatever sync variant you are running: always make sure you know what you are doing.
Only for a properly developed and verified sync configuration directly click the Synchronize button.
The same holds for (silently) running sync configurations saved as a *.ffs_batch file, as those, just like when directly clicking the Synchronize button, do not pause between the Compare and Synchronize phase.
- Posts: 2
- Joined: 21 Mar 2026
Agreed 100%. It is just a matter of terminology. It was my mistake. The software is great. However, I still think that a warning would be of benefit. That would be relatively easy to do within the user interface.
