One important aspect of a backup program is a coherent story for restore and disaster recovery. I think that’s often the trickier part.
Absolutely valid.
I don’t see how One-Way sync + versioning (natively or via file system snapshots) could be defined as anything other than a “backup”.
Sure you could configure it in a raid like fashion where you have lower data security but you could also configure nearly any backup application similarly poorly for safety.
You’re absolutely right, retaining a duplicate copy of a file is a backup regardless of the method involved.
It doesn’t seem as though this thread, and others like it, have been debating much about what constitutes a valid backup, but rather mostly debating whether or not Syncthing is an appropriate tool for making backups.
For me, a beneficial side effect of Syncthing mirroring my data across multiple devices has been that it also satisfies the “3-2-1 rule” for a good backup strategy:
- 3 copies of the data
- 2 or more storage media types
- 1 offsite copy
However, an accidental file deletion would ripple across my “pool” of Syncthing devices pretty quickly – certainly faster than I could get to an offsite device.
Purpose-built backup software has some common features including:
- Scheduling
- Integrity checks
- Compression
- Deduplication
- Review and restore tool
Syncthing excels at what it was designed to do and intended for, so not including the backup features above isn’t a fault.
File versioning in Syncthing can be used to simulate an incremental backup system, but…
- … being able to easily review and selectively restore one or more files is what most users expect.
- … files under Syncthing’s versions folder are at risk of accidental deletion and bit rot without warning.
- … without deduplication and compression, retaining more than a few days worth of backups could require a lot of extra storage.
At my employer, a mission critical file server has been backed up daily exactly 1,500 times (so far). Millions of text files (emails) often repeatedly change by just a few bytes as they are marked, tagged and moved around. Without deduplication and compression, the total storage requirement could be over 200 TiB, but it consumes just 1.2 TiB.
Part of my backup routine includes checking the integrity of the snapshots, but repeated full restores as a test is impractical due to the number of files involved. So the ability to verify that a snapshot matches its signature is a huge time saver.
I can select a snapshot number to restore, search by filename, etc., plus there’s no need to rename a million files afterwards (to remove the timestamp added by Syncthing).
That being said, I use Syncthing as part of my total backup strategy for my most frequently used files which are backed up to remote storage.
The advantage of software that’s designed for backups is that it makes it more difficult to accidentally shoot one’s own foot. 
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Almost. I am the thread starter.
Syncthing is not a backup tool. Everyone here agrees with that, I think. (And if someone does NOT agree, this thread is not for you.) One can use it to do “poor man’s backup” (using file versioning on a machine you never ever modify files on yourself), but that still does not make it a backup tool, and you explained very well what it lacks to be that.
This thread was started for one specific purpose. On the front page of the Syncthing website we have this:
My point is this: Some people (Not the people in this thread. Others.) might be mislead by that sentence into believing that Syncthing is a backup tool. So I still propose that this sentence is expanded SLIGHTLY to, IMHO, make it clearer:
“synchronize them with your server so you can do backup there.”
Nothing else. 
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To be honest, and speaking from experience, Syncthing with file versioning enabled is probably enough of a backup for average non-technical home users. They aren’t capable of configuring anything more advanced and robust anyway, and the alternative for them is usually not using any backup at all.
Just for the record, you can find many interesting/amusing/tragic topics if you search for https://forum.syncthing.net/search?q=backup 
.
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According to Statista and Backblaze…
Percentage of users and their chosen backup storage medium:
- Cloud: 58%
- External hard drive: 38%
- NAS: 5%
As of 2023, the percentage of users and frequency of backups:
- daily: 11%
- weekly: 12%
- monthly: 22%
- yearly: 24%
- year+: 13%
- never: 18%
Since there has to be at least two instances of Syncthing talking to each other, and it would fall within the “daily” backup category, it doesn’t appear that Syncthing would appeal to the majority of home users as a backup solution.
Most of the people I’ve met who do want backups usually buy a USB drive and install the free software that’s often found on the drive. The lack of interest in researching and choosing backup software is understandable given the overwhelming number of options available.
One individual I know had a USB drive plugged into a Windows PC for about 2 years. The bundled backup software had been installed and was running. One day while I was helping replace the PC’s bad power supply, I checked the USB drive to see if it was okay. The only thing I found on the drive was the backup software installer and no sign of any backups – it turned out that he’d assumed that backups would automatically start as soon as the backup software was running.
(Also according to the survey results, at least 10% of the users who backed up to cloud storage didn’t know what was covered in the backups.)
Past few years of Backblaze’s annual computer backup awareness survey results:
- 2018: Computer Backup Awareness in 2018: Getting Better and Getting Worse
- 2019: More People Than Ever Backing Up According to Our Survey
- 2020: Daily Backups Hit an All Time High
- 2021: The State of Backups: Who’s Most at Risk
- 2022: The 2022 Backup Survey: 54% Report Data Loss With Only 10% Backing Up Daily
- 2023: 2023 State of the Backup: As Data Needs Grow, Backups Need to Fill the Gaps
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At least they tried… I know someone who had been hit by ransomware and because the files were work-related, they had no choice but to pay the ransom to get them back. However, even after such an incident, they still don’t do regular backups (except for maybe copying some files onto a USB drive from time to time, but they usually forget to do that anyway).
I have a similar use case, where many computers sync to a central one via Syncthing and this central one does regular local and offsite backups.
That gives me a simple and robust 3,2,1 backup strategy.
The wording on the webpage is thus also accurate for me.
About the suggestion of making a “backup” folder type: I’d would have a use for this personally. Basically: rsync with Syncthing device discovery would actually be a great use case. Maybe that could be a spin-off separate program through.
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Yes exactly. I’d much prefer use in the existing tool simply out of convenience as it is already running.
I have actually been thinking about running a second container on a schedule just for backing up. May or may not set that up as it has its own problems.
So true. Putting in the effort is the biggest hurdle. I mentioned the problem to him and then helped configure a backup schedule.
I’ve experienced a number of situations where someone has an external drive for backups. Eventually runs out of space on the system drive. Proceeds to move important files off the system drive and onto the external “backup” drive in order to free up space for more files on the system drive – somehow it makes logical sense to the users who do it.
In one particular instance at work, a colleague had two PCs where one backed up to the other over a LAN. One day, to free up space, files were deleted from PC1, leaving the “backup” on PC2. The problem was that the daily backup process was still active, slowly overwriting older backups. About three months later the owner of the deleted files needed them. Ended up sending the drive to a data recovery service… ~$2K service charge and no data was recoverable. I’d previously offered to offload backups to a department file server, but it wasn’t of any interest.
(Backblaze’s annual survey includes the statistic that more than half of the participants have lost data in the past year.)
The restic backup application is written in Golang. In theory we could integrate or call the executable in Syncthing and expose a backup share. Then all the restic magic can happen about packing the backup, prune old backups, encrypting the backup. But that is just a wild idea. I think when this feature is designed it will blow up Syncthings ideas.
And there is still nothing wrong with the US Navy - KISS principle or “Unix philosophy - Do One Thing and Do It Well”.
Let one program do a task good and well, including keeping its documentation/forum and community in sublime conditions which in my opinion is even more needed.
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Syncthing is a backup program—especially when used in parallel with its version filling system.
It keeps additional copies of files across devices (including older editions) that helps provide some safety if one or more machines are no long usable.
This is redundancy, not backup. There is a big difference between the two (e.g. see https://serverfault.com/questions/726983/do-i-still-need-a-backup-if-i-have-a-redudant-storage-system-with-rollback-capab).
File versioning is backup, although not full backup, just per file backup. I personally think it’s still more than enough for the average user (for whom specialised backup solutions are too complicated to use anyway).
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I think the way it works is
Syncthing is a file synchronisation program
And when you make a “zip” file of that folder on the other machine, now you have a backup.
Syncthing won’t make those zip files. If you delete a file, it gets deleted on the other side, that’s file synchronisation technology.
And for me that’s more than enough. I do my regular “zip” files manually, and feel safer this way, I compare their sizes with last week’s, and I can see if any discrepancy, and I keep the pulse on my files.
I let Syncthing only take care of file synchronisation, it does one thing and does it well.
This idea has some appeal, but I fear that it would not be well understood and would be a source of further confusion. “I set the share to ‘Backup’ mode and it didn’t back up!”
It may be worth further discussion, because it could be useful.
But I lean more toward “Do ONE job” and KISS.
I agree that something like this wording is a big improvement and helps clarify the niche that Syncthing is intended to fill.