Sync keeps two places identical. Backup keeps a history. The words get used interchangeably, and the gap between them is exactly where people lose files while believing they were protected.
What sync actually promises
A sync folder makes the same files appear on your laptop, your desktop and your phone, and keeps them current everywhere. Edit a document at work and it is already updated at home. This is genuinely useful, and for day-to-day working it is the right tool.
But the promise is symmetry, and symmetry cuts both ways. Delete a folder on one machine and sync deletes it everywhere, promptly and correctly. Overwrite the good version of a file with a bad one and every device now holds the bad one. The system is not malfunctioning when this happens. Propagating your changes is the entire job.
The failures sync cannot save you from
Deletion. The most common data loss event is someone removing the wrong thing, and a pure sync setup replicates the removal at the speed of your connection.
Overwrites. Saving over the wrong file, an export that replaced the original, a colleague’s edit landing on top of yours - sync ships the new state and the old one is gone.
Ransomware. Malware that encrypts your disk encrypts the sync folder with it, and the client dutifully uploads the encrypted versions. The mirror is then a perfect copy of the damage. Our guide to file versioning as the undo button covers this scenario properly, because it deserves its own treatment.
What backup adds
Backup keeps states you have already left. Yesterday’s version of the document, last month’s copy of the folder, the file as it was before this morning’s mistake. The property that matters is that old states are kept on purpose, so a bad change today cannot reach into the past and destroy them.
That is the whole distinction. Sync answers “what is the current state, everywhere?” Backup answers “what did this look like before?”
Do you need backup if you already sync?
Mostly yes, and the honest answer is that the two features have been growing towards each other for years.
Storage that keeps file versions closes most of the gap for everyday mistakes: when a file changes, the previous version is kept, and restoring it is a click rather than a recovery project. A recoverable trash does the same for deletions. Our sync works this way - the desktop app keeps folders current in the usual manner, and the storage behind it retains prior versions when files change, so an overwrite is an inconvenience rather than a loss. The desktop app covers Mac, Windows and Linux.
What versions do not replace is a genuinely separate copy. If the account itself is the thing that fails - credentials stolen, or simply closed in anger - a second copy elsewhere is what saves you. The 3-2-1 rule is the standard way to think about that, and it is less work than its reputation suggests.
A reasonable setup, concretely
For most people the workable arrangement is: a sync folder for the files you touch weekly, versioning on so mistakes are reversible, and a periodic true backup of the irreplaceable subset - photos, documents, the tax archive - to somewhere that is not any of your sync endpoints.
Phones deserve a special mention, because camera rolls are the largest collection of genuinely irreplaceable files most people own, and they are usually on the weakest protection. Automatic photo backup covers doing that properly.
For servers and machines nobody sits at, sync is the wrong shape entirely - you want scheduled backup to object storage instead.
The test worth applying
Ask of your current setup: if I deleted a folder right now and noticed in three weeks, what would happen? If the honest answer is “it would be gone everywhere”, you have sync, not backup, and the gap is worth closing this week rather than after it costs you something.
Frequently asked questions
What is the difference between backup and sync?
Sync keeps the same files identical across your devices, so changes and deletions appear everywhere at once. Backup keeps older states on purpose, so a mistake today cannot destroy yesterday's copy. Sync is for availability, backup is for recovery.
Is a sync folder like Dropbox a backup?
Not by itself. A sync folder mirrors deletions and overwrites as faithfully as any other change. It only starts to behave like a backup when the storage behind it keeps version history and a recoverable trash.
Do I still need a backup if my storage keeps file versions?
Versions cover everyday mistakes such as overwrites and accidental deletions. For failures that affect the whole account, a separate copy somewhere else is still the safety net, which is what the 3-2-1 rule describes.
